diff --git a/accessible/src/base/AccIterator.cpp b/accessible/src/base/AccIterator.cpp
index bdf4b7ca3a56..a317820eec33 100644
--- a/accessible/src/base/AccIterator.cpp
+++ b/accessible/src/base/AccIterator.cpp
@@ -82,7 +82,7 @@ RelatedAccIterator::
 {
   mBindingParent = aDependentContent->GetBindingParent();
   nsIAtom* IDAttr = mBindingParent ?
-    nsGkAtoms::anonid : aDependentContent->GetIDAttributeName();
+    nsGkAtoms::anonid : nsGkAtoms::id;
 
   nsAutoString id;
   if (aDependentContent->GetAttr(kNameSpaceID_None, IDAttr, id))
diff --git a/accessible/src/base/nsCoreUtils.cpp b/accessible/src/base/nsCoreUtils.cpp
index c0771687faf6..621492037a07 100644
--- a/accessible/src/base/nsCoreUtils.cpp
+++ b/accessible/src/base/nsCoreUtils.cpp
@@ -456,8 +456,7 @@ nsCoreUtils::IsErrorPage(nsIDocument *aDocument)
 bool
 nsCoreUtils::GetID(nsIContent *aContent, nsAString& aID)
 {
-  nsIAtom *idAttribute = aContent->GetIDAttributeName();
-  return idAttribute ? aContent->GetAttr(kNameSpaceID_None, idAttribute, aID) : false;
+  return aContent->GetAttr(kNameSpaceID_None, nsGkAtoms::id, aID);
 }
 
 bool
diff --git a/accessible/src/generic/Accessible.cpp b/accessible/src/generic/Accessible.cpp
index 3d4a11232ba8..f2b64bbe878a 100644
--- a/accessible/src/generic/Accessible.cpp
+++ b/accessible/src/generic/Accessible.cpp
@@ -1555,7 +1555,7 @@ Accessible::ApplyARIAState(uint64_t* aState) const
     if (mRoleMapEntry->role != roles::NOTHING)
       *aState &= ~states::READONLY;
 
-    if (mContent->HasAttr(kNameSpaceID_None, mContent->GetIDAttributeName())) {
+    if (mContent->HasID()) {
       // If has a role & ID and aria-activedescendant on the container, assume focusable
       nsIContent *ancestorContent = mContent;
       while ((ancestorContent = ancestorContent->GetParent()) != nullptr) {
diff --git a/content/base/public/Element.h b/content/base/public/Element.h
index 5eb59bde5d59..3e58f0e6c989 100644
--- a/content/base/public/Element.h
+++ b/content/base/public/Element.h
@@ -279,13 +279,6 @@ class Element : public FragmentOrElement
   virtual nsChangeHint GetAttributeChangeHint(const nsIAtom* aAttribute,
                                               int32_t aModType) const;
 
-  /**
-   * Returns an atom holding the name of the "class" attribute on this
-   * content node (if applicable).  Returns null if there is no
-   * "class" attribute for this type of content node.
-   */
-  virtual nsIAtom *GetClassAttributeName() const;
-
   inline Directionality GetDirectionality() const {
     if (HasFlag(NODE_HAS_DIRECTION_RTL)) {
       return eDir_RTL;
@@ -587,8 +580,20 @@ class Element : public FragmentOrElement
   {
     SetAttr(kNameSpaceID_None, nsGkAtoms::id, aId, true);
   }
+  void GetClassName(nsAString& aClassName)
+  {
+    GetAttr(kNameSpaceID_None, nsGkAtoms::_class, aClassName);
+  }
+  void GetClassName(DOMString& aClassName)
+  {
+    GetAttr(kNameSpaceID_None, nsGkAtoms::_class, aClassName);
+  }
+  void SetClassName(const nsAString& aClassName)
+  {
+    SetAttr(kNameSpaceID_None, nsGkAtoms::_class, aClassName, true);
+  }
 
-  nsDOMTokenList* GetClassList();
+  nsDOMTokenList* ClassList();
   nsDOMAttributeMap* Attributes()
   {
     nsDOMSlots* slots = DOMSlots();
@@ -862,8 +867,6 @@ class Element : public FragmentOrElement
     const nsAttrValue* mValue;
   };
 
-  // Be careful when using this method. This does *NOT* handle
-  // XUL prototypes. You may want to use GetAttrInfo.
   const nsAttrValue* GetParsedAttr(nsIAtom* aAttr) const
   {
     return mAttrsAndChildren.GetAttr(aAttr);
@@ -1128,8 +1131,7 @@ class Element : public FragmentOrElement
    * Add/remove this element to the documents id cache
    */
   void AddToIdTable(nsIAtom* aId);
-  void RemoveFromIdTable(); // checks HasID() and uses DoGetID()
-  void RemoveFromIdTable(nsIAtom* aId);
+  void RemoveFromIdTable();
 
   /**
    * Functions to carry out event default actions for links of all types
@@ -1364,6 +1366,26 @@ NS_IMETHOD GetTagName(nsAString& aTagName) MOZ_FINAL                          \
   Element::GetTagName(aTagName);                                              \
   return NS_OK;                                                               \
 }                                                                             \
+NS_IMETHOD GetId(nsAString& aId) MOZ_FINAL                                    \
+{                                                                             \
+  Element::GetId(aId);                                                        \
+  return NS_OK;                                                               \
+}                                                                             \
+NS_IMETHOD SetId(const nsAString& aId) MOZ_FINAL                              \
+{                                                                             \
+  Element::SetId(aId);                                                        \
+  return NS_OK;                                                               \
+}                                                                             \
+NS_IMETHOD GetClassName(nsAString& aClassName) MOZ_FINAL                      \
+{                                                                             \
+  Element::GetClassName(aClassName);                                          \
+  return NS_OK;                                                               \
+}                                                                             \
+NS_IMETHOD SetClassName(const nsAString& aClassName) MOZ_FINAL                \
+{                                                                             \
+  Element::SetClassName(aClassName);                                          \
+  return NS_OK;                                                               \
+}                                                                             \
 NS_IMETHOD GetClassList(nsISupports** aClassList) MOZ_FINAL                   \
 {                                                                             \
   Element::GetClassList(aClassList);                                          \
diff --git a/content/base/public/FragmentOrElement.h b/content/base/public/FragmentOrElement.h
index e73f9b9342f3..0576e992b400 100644
--- a/content/base/public/FragmentOrElement.h
+++ b/content/base/public/FragmentOrElement.h
@@ -222,7 +222,6 @@ class FragmentOrElement : public nsIContent
   virtual void DestroyContent() MOZ_OVERRIDE;
   virtual void SaveSubtreeState() MOZ_OVERRIDE;
 
-  virtual const nsAttrValue* DoGetClasses() const MOZ_OVERRIDE;
   NS_IMETHOD WalkContentStyleRules(nsRuleWalker* aRuleWalker) MOZ_OVERRIDE;
 
   nsIHTMLCollection* Children();
diff --git a/content/base/public/nsIContent.h b/content/base/public/nsIContent.h
index bed0209ade26..4922f729ca0e 100644
--- a/content/base/public/nsIContent.h
+++ b/content/base/public/nsIContent.h
@@ -320,13 +320,6 @@ class nsIContent : public nsINode {
            GetBindingParent();
   }
 
-  /**
-   * Returns an atom holding the name of the attribute of type ID on
-   * this content node (if applicable).  Returns null for non-element
-   * content nodes.
-   */
-  virtual nsIAtom *GetIDAttributeName() const = 0;
-
   /**
    * Set attribute values. All attribute values are assumed to have a
    * canonical string representation that can be used for these
@@ -831,8 +824,7 @@ class nsIContent : public nsINode {
 
   /**
    * Get the ID of this content node (the atom corresponding to the
-   * value of the null-namespace attribute whose name is given by
-   * GetIDAttributeName().  This may be null if there is no ID.
+   * value of the id attribute).  This may be null if there is no ID.
    */
   nsIAtom* GetID() const {
     if (HasID()) {
@@ -843,8 +835,7 @@ class nsIContent : public nsINode {
 
   /**
    * Get the class list of this content node (this corresponds to the
-   * value of the null-namespace attribute whose name is given by
-   * GetClassAttributeName()).  This may be null if there are no
+   * value of the class attribute).  This may be null if there are no
    * classes, but that's not guaranteed.
    */
   const nsAttrValue* GetClasses() const {
@@ -957,14 +948,14 @@ class nsIContent : public nsINode {
    * Hook for implementing GetID.  This is guaranteed to only be
    * called if HasID() is true.
    */
-  virtual nsIAtom* DoGetID() const = 0;
+  nsIAtom* DoGetID() const;
 
 private:
   /**
    * Hook for implementing GetClasses.  This is guaranteed to only be
    * called if the NODE_MAY_HAVE_CLASS flag is set.
    */
-  virtual const nsAttrValue* DoGetClasses() const = 0;
+  const nsAttrValue* DoGetClasses() const;
 
 public:
 #ifdef DEBUG
diff --git a/content/base/public/nsINodeInfo.h b/content/base/public/nsINodeInfo.h
index 53e695b56609..e73bbe1e7a11 100644
--- a/content/base/public/nsINodeInfo.h
+++ b/content/base/public/nsINodeInfo.h
@@ -160,22 +160,6 @@ class nsINodeInfo : public nsISupports
     return mInner.mExtraName;
   }
 
-  /*
-   * Get and set the ID attribute atom for this node.
-   * See http://www.w3.org/TR/1998/REC-xml-19980210#sec-attribute-types
-   * for the definition of an ID attribute.
-   *
-   */
-  nsIAtom* GetIDAttributeAtom() const
-  {
-    return mIDAttributeAtom;
-  }
-
-  void SetIDAttributeAtom(nsIAtom* aID)
-  {
-    mIDAttributeAtom = aID;
-  }
-
   /**
    * Get the owning node info manager. Only to be used inside Gecko, you can't
    * really do anything with the pointer outside Gecko anyway.
@@ -330,7 +314,6 @@ class nsINodeInfo : public nsISupports
 
   nsNodeInfoInner mInner;
 
-  nsCOMPtr<nsIAtom> mIDAttributeAtom;
   nsRefPtr<nsNodeInfoManager> mOwnerManager;
 
   /*
diff --git a/content/base/src/Attr.cpp b/content/base/src/Attr.cpp
index 76f7f7a79e4d..ecc43cf9cdb1 100644
--- a/content/base/src/Attr.cpp
+++ b/content/base/src/Attr.cpp
@@ -321,19 +321,7 @@ Attr::SetTextContentInternal(const nsAString& aTextContent,
 NS_IMETHODIMP
 Attr::GetIsId(bool* aReturn)
 {
-  Element* element = GetElement();
-  if (!element) {
-    *aReturn = false;
-    return NS_OK;
-  }
-
-  nsIAtom* idAtom = element->GetIDAttributeName();
-  if (!idAtom) {
-    *aReturn = false;
-    return NS_OK;
-  }
-
-  *aReturn = mNodeInfo->Equals(idAtom, kNameSpaceID_None);
+  *aReturn = mNodeInfo->Equals(nsGkAtoms::id, kNameSpaceID_None);
   return NS_OK;
 }
 
diff --git a/content/base/src/DocumentFragment.cpp b/content/base/src/DocumentFragment.cpp
index ac185d0aced5..ace0e4c968ad 100644
--- a/content/base/src/DocumentFragment.cpp
+++ b/content/base/src/DocumentFragment.cpp
@@ -35,18 +35,6 @@ DocumentFragment::IsNodeOfType(uint32_t aFlags) const
   return !(aFlags & ~(eCONTENT | eDOCUMENT_FRAGMENT));
 }
 
-nsIAtom*
-DocumentFragment::DoGetID() const
-{
-  return nullptr;  
-}
-
-nsIAtom*
-DocumentFragment::GetIDAttributeName() const
-{
-  return nullptr;
-}
-
 NS_IMETHODIMP
 DocumentFragment::QuerySelector(const nsAString& aSelector,
                                 nsIDOMElement **aReturn)
diff --git a/content/base/src/DocumentFragment.h b/content/base/src/DocumentFragment.h
index 1e4fc9e5ce34..5c932dda3f42 100644
--- a/content/base/src/DocumentFragment.h
+++ b/content/base/src/DocumentFragment.h
@@ -103,9 +103,6 @@ class DocumentFragment : public FragmentOrElement,
 
   virtual nsIDOMNode* AsDOMNode() MOZ_OVERRIDE { return this; }
 
-  virtual nsIAtom* DoGetID() const MOZ_OVERRIDE;
-  virtual nsIAtom *GetIDAttributeName() const MOZ_OVERRIDE;
-
   virtual nsresult BindToTree(nsIDocument* aDocument, nsIContent* aParent,
                               nsIContent* aBindingParent,
                               bool aCompileEventHandlers) MOZ_OVERRIDE
diff --git a/content/base/src/Element.cpp b/content/base/src/Element.cpp
index 707419957de6..a527f0dceb20 100644
--- a/content/base/src/Element.cpp
+++ b/content/base/src/Element.cpp
@@ -66,6 +66,7 @@
 #ifdef MOZ_XUL
 #include "nsXULElement.h"
 #endif /* MOZ_XUL */
+#include "nsSVGElement.h"
 #include "nsFrameManager.h"
 #include "nsFrameSelection.h"
 #ifdef DEBUG
@@ -138,6 +139,32 @@
 using namespace mozilla;
 using namespace mozilla::dom;
 
+nsIAtom*
+nsIContent::DoGetID() const
+{
+  MOZ_ASSERT(HasID(), "Unexpected call");
+  MOZ_ASSERT(IsElement(), "Only elements can have IDs");
+
+  return AsElement()->GetParsedAttr(nsGkAtoms::id)->GetAtomValue();
+}
+
+const nsAttrValue*
+nsIContent::DoGetClasses() const
+{
+  MOZ_ASSERT(HasFlag(NODE_MAY_HAVE_CLASS), "Unexpected call");
+  MOZ_ASSERT(IsElement(), "Only elements can have classes");
+
+  if (IsSVG()) {
+    const nsAttrValue* animClass =
+      static_cast<const nsSVGElement*>(this)->GetAnimatedClassName();
+    if (animClass) {
+      return animClass;
+    }
+  }
+
+  return AsElement()->GetParsedAttr(nsGkAtoms::_class);
+}
+
 NS_IMETHODIMP
 Element::QueryInterface(REFNSIID aIID, void** aInstancePtr)
 {
@@ -469,15 +496,12 @@ Element::WrapObject(JSContext *aCx)
 }
 
 nsDOMTokenList*
-Element::GetClassList()
+Element::ClassList()
 {
-  Element::nsDOMSlots *slots = DOMSlots();
+  Element::nsDOMSlots* slots = DOMSlots();
 
   if (!slots->mClassList) {
-    nsIAtom* classAttr = GetClassAttributeName();
-    if (classAttr) {
-      slots->mClassList = new nsDOMTokenList(this, classAttr);
-    }
+    slots->mClassList = new nsDOMTokenList(this, nsGkAtoms::_class);
   }
 
   return slots->mClassList;
@@ -486,7 +510,7 @@ Element::GetClassList()
 void
 Element::GetClassList(nsISupports** aClassList)
 {
-  NS_IF_ADDREF(*aClassList = GetClassList());
+  NS_ADDREF(*aClassList = ClassList());
 }
 
 already_AddRefed<nsIHTMLCollection>
@@ -739,31 +763,22 @@ Element::AddToIdTable(nsIAtom* aId)
 void
 Element::RemoveFromIdTable()
 {
-  if (HasID()) {
-    RemoveFromIdTable(DoGetID());
+  if (!HasID()) {
+    return;
   }
-}
 
-void
-Element::RemoveFromIdTable(nsIAtom* aId)
-{
-  NS_ASSERTION(HasID(), "Node doesn't have an ID?");
+  nsIAtom* id = DoGetID();
   if (HasFlag(NODE_IS_IN_SHADOW_TREE)) {
     ShadowRoot* containingShadow = GetContainingShadow();
     // Check for containingShadow because it may have
     // been deleted during unlinking.
     if (containingShadow) {
-      containingShadow->RemoveFromIdTable(this, aId);
+      containingShadow->RemoveFromIdTable(this, id);
     }
   } else {
     nsIDocument* doc = GetCurrentDoc();
     if (doc && (!IsInAnonymousSubtree() || doc->IsXUL())) {
-      // id can be null during mutation events evilness. Also, XUL elements
-      // loose their proto attributes during cc-unlink, so this can happen
-      // during cc-unlink too.
-      if (aId) {
-        doc->RemoveFromIdTable(this, aId);
-      }
+      doc->RemoveFromIdTable(this, id);
     }
   }
 }
@@ -1573,12 +1588,6 @@ Element::GetAttributeChangeHint(const nsIAtom* aAttribute,
   return nsChangeHint(0);
 }
 
-nsIAtom *
-Element::GetClassAttributeName() const
-{
-  return nullptr;
-}
-
 bool
 Element::FindAttributeDependence(const nsIAtom* aAttribute,
                                  const MappedAttributeEntry* const aMaps[],
@@ -2056,6 +2065,27 @@ Element::ParseAttribute(int32_t aNamespaceID,
                         const nsAString& aValue,
                         nsAttrValue& aResult)
 {
+  if (aNamespaceID == kNameSpaceID_None) {
+    if (aAttribute == nsGkAtoms::_class) {
+      SetFlags(NODE_MAY_HAVE_CLASS);
+      aResult.ParseAtomArray(aValue);
+      return true;
+    }
+    if (aAttribute == nsGkAtoms::id) {
+      // Store id as an atom.  id="" means that the element has no id,
+      // not that it has an emptystring as the id.
+      RemoveFromIdTable();
+      if (aValue.IsEmpty()) {
+        ClearHasID();
+        return false;
+      }
+      aResult.ParseAtom(aValue);
+      SetHasID();
+      AddToIdTable(aResult.GetAtomValue());
+      return true;
+    }
+  }
+
   return false;
 }
 
@@ -2171,6 +2201,12 @@ Element::UnsetAttr(int32_t aNameSpaceID, nsIAtom* aName,
   // react to unexpected attribute changes.
   nsMutationGuard::DidMutate();
 
+  if (aName == nsGkAtoms::id && aNameSpaceID == kNameSpaceID_None) {
+    // Have to do this before clearing flag. See RemoveFromIdTable
+    RemoveFromIdTable();
+    ClearHasID();
+  }
+
   bool hadValidDir = false;
   bool hadDirAuto = false;
 
diff --git a/content/base/src/FragmentOrElement.cpp b/content/base/src/FragmentOrElement.cpp
index 0a15e4c3435d..9046ebb80bb3 100644
--- a/content/base/src/FragmentOrElement.cpp
+++ b/content/base/src/FragmentOrElement.cpp
@@ -886,13 +886,6 @@ nsIContent::IsFocusableInternal(int32_t* aTabIndex, bool aWithMouse)
   return false;
 }
 
-const nsAttrValue*
-FragmentOrElement::DoGetClasses() const
-{
-  NS_NOTREACHED("Shouldn't ever be called");
-  return nullptr;
-}
-
 NS_IMETHODIMP
 FragmentOrElement::WalkContentStyleRules(nsRuleWalker* aRuleWalker)
 {
diff --git a/content/base/src/nsGenericDOMDataNode.cpp b/content/base/src/nsGenericDOMDataNode.cpp
index 58271510d528..db837d9b3a09 100644
--- a/content/base/src/nsGenericDOMDataNode.cpp
+++ b/content/base/src/nsGenericDOMDataNode.cpp
@@ -590,12 +590,6 @@ nsGenericDOMDataNode::GetChildren(uint32_t aFilter)
   return nullptr;
 }
 
-nsIAtom *
-nsGenericDOMDataNode::GetIDAttributeName() const
-{
-  return nullptr;
-}
-
 nsresult
 nsGenericDOMDataNode::SetAttr(int32_t aNameSpaceID, nsIAtom* aAttr,
                               nsIAtom* aPrefix, const nsAString& aValue,
@@ -1070,19 +1064,6 @@ nsGenericDOMDataNode::GetCurrentValueAtom()
   return NS_NewAtom(val);
 }
 
-nsIAtom*
-nsGenericDOMDataNode::DoGetID() const
-{
-  return nullptr;
-}
-
-const nsAttrValue*
-nsGenericDOMDataNode::DoGetClasses() const
-{
-  NS_NOTREACHED("Shouldn't ever be called");
-  return nullptr;
-}
-
 NS_IMETHODIMP
 nsGenericDOMDataNode::WalkContentStyleRules(nsRuleWalker* aRuleWalker)
 {
@@ -1103,12 +1084,6 @@ nsGenericDOMDataNode::GetAttributeChangeHint(const nsIAtom* aAttribute,
   return nsChangeHint(0);
 }
 
-nsIAtom*
-nsGenericDOMDataNode::GetClassAttributeName() const
-{
-  return nullptr;
-}
-
 size_t
 nsGenericDOMDataNode::SizeOfExcludingThis(MallocSizeOf aMallocSizeOf) const
 {
diff --git a/content/base/src/nsGenericDOMDataNode.h b/content/base/src/nsGenericDOMDataNode.h
index 3df7e0eda656..81ecd2abdb05 100644
--- a/content/base/src/nsGenericDOMDataNode.h
+++ b/content/base/src/nsGenericDOMDataNode.h
@@ -115,7 +115,6 @@ class nsGenericDOMDataNode : public nsIContent
 
   virtual already_AddRefed<nsINodeList> GetChildren(uint32_t aFilter) MOZ_OVERRIDE;
 
-  virtual nsIAtom *GetIDAttributeName() const MOZ_OVERRIDE;
 
   nsresult SetAttr(int32_t aNameSpaceID, nsIAtom* aName,
                    const nsAString& aValue, bool aNotify)
@@ -170,13 +169,10 @@ class nsGenericDOMDataNode : public nsIContent
   virtual mozilla::dom::CustomElementData* GetCustomElementData() const MOZ_OVERRIDE;
   virtual void SetCustomElementData(mozilla::dom::CustomElementData* aData) MOZ_OVERRIDE;
 
-  virtual nsIAtom* DoGetID() const MOZ_OVERRIDE;
-  virtual const nsAttrValue* DoGetClasses() const MOZ_OVERRIDE;
   NS_IMETHOD WalkContentStyleRules(nsRuleWalker* aRuleWalker) MOZ_OVERRIDE;
   NS_IMETHOD_(bool) IsAttributeMapped(const nsIAtom* aAttribute) const;
   virtual nsChangeHint GetAttributeChangeHint(const nsIAtom* aAttribute,
                                               int32_t aModType) const;
-  virtual nsIAtom *GetClassAttributeName() const;
 
   virtual nsresult Clone(nsINodeInfo *aNodeInfo, nsINode **aResult) const MOZ_OVERRIDE
   {
diff --git a/content/base/src/nsStyledElement.cpp b/content/base/src/nsStyledElement.cpp
index 6698157a7a6a..9cb112f9b152 100644
--- a/content/base/src/nsStyledElement.cpp
+++ b/content/base/src/nsStyledElement.cpp
@@ -28,106 +28,22 @@ using namespace mozilla::dom;
 //----------------------------------------------------------------------
 // nsIContent methods
 
-nsIAtom*
-nsStyledElementNotElementCSSInlineStyle::GetClassAttributeName() const
-{
-  return nsGkAtoms::_class;
-}
-
-nsIAtom*
-nsStyledElementNotElementCSSInlineStyle::GetIDAttributeName() const
-{
-  return nsGkAtoms::id;
-}
-
-nsIAtom*
-nsStyledElementNotElementCSSInlineStyle::DoGetID() const
-{
-  NS_ASSERTION(HasID(), "Unexpected call");
-
-  // The nullcheck here is needed because Element::UnsetAttr calls
-  // out to various code between removing the attribute and we get a chance to
-  // ClearHasID().
-
-  const nsAttrValue* attr = mAttrsAndChildren.GetAttr(nsGkAtoms::id);
-
-  return attr ? attr->GetAtomValue() : nullptr;
-}
-
-const nsAttrValue*
-nsStyledElementNotElementCSSInlineStyle::DoGetClasses() const
-{
-  NS_ASSERTION(HasFlag(NODE_MAY_HAVE_CLASS), "Unexpected call");
-  return mAttrsAndChildren.GetAttr(nsGkAtoms::_class);
-}
-
 bool
 nsStyledElementNotElementCSSInlineStyle::ParseAttribute(int32_t aNamespaceID,
                                                         nsIAtom* aAttribute,
                                                         const nsAString& aValue,
                                                         nsAttrValue& aResult)
 {
-  if (aNamespaceID == kNameSpaceID_None) {
-    if (aAttribute == nsGkAtoms::style) {
-      SetMayHaveStyle();
-      ParseStyleAttribute(aValue, aResult, false);
-      return true;
-    }
-    if (aAttribute == nsGkAtoms::_class) {
-      SetFlags(NODE_MAY_HAVE_CLASS);
-      aResult.ParseAtomArray(aValue);
-      return true;
-    }
-    if (aAttribute == nsGkAtoms::id) {
-      // Store id as an atom.  id="" means that the element has no id,
-      // not that it has an emptystring as the id.
-      RemoveFromIdTable();
-      if (aValue.IsEmpty()) {
-        ClearHasID();
-        return false;
-      }
-      aResult.ParseAtom(aValue);
-      SetHasID();
-      AddToIdTable(aResult.GetAtomValue());
-      return true;
-    }
+  if (aAttribute == nsGkAtoms::style && aNamespaceID == kNameSpaceID_None) {
+    SetMayHaveStyle();
+    ParseStyleAttribute(aValue, aResult, false);
+    return true;
   }
 
   return nsStyledElementBase::ParseAttribute(aNamespaceID, aAttribute, aValue,
                                              aResult);
 }
 
-nsresult
-nsStyledElementNotElementCSSInlineStyle::UnsetAttr(int32_t aNameSpaceID,
-                                                   nsIAtom* aAttribute,
-                                                   bool aNotify)
-{
-  nsAutoScriptBlocker scriptBlocker;
-  if (aAttribute == nsGkAtoms::id && aNameSpaceID == kNameSpaceID_None) {
-    // Have to do this before clearing flag. See RemoveFromIdTable
-    RemoveFromIdTable();
-  }
-
-  return Element::UnsetAttr(aNameSpaceID, aAttribute, aNotify);
-}
-
-nsresult
-nsStyledElementNotElementCSSInlineStyle::AfterSetAttr(int32_t aNamespaceID,
-                                                      nsIAtom* aAttribute,
-                                                      const nsAttrValue* aValue,
-                                                      bool aNotify)
-{
-  if (aNamespaceID == kNameSpaceID_None && !aValue &&
-      aAttribute == nsGkAtoms::id) {
-    // The id has been removed when calling UnsetAttr but we kept it because
-    // the id is used for some layout stuff between UnsetAttr and AfterSetAttr.
-    // Now. the id is really removed so it would not be safe to keep this flag.
-    ClearHasID();
-  }
-
-  return Element::AfterSetAttr(aNamespaceID, aAttribute, aValue, aNotify);
-}
-
 nsresult
 nsStyledElementNotElementCSSInlineStyle::SetInlineStyleRule(css::StyleRule* aStyleRule,
                                                             const nsAString* aSerialized,
diff --git a/content/base/src/nsStyledElement.h b/content/base/src/nsStyledElement.h
index 832b986772af..3f381c1da031 100644
--- a/content/base/src/nsStyledElement.h
+++ b/content/base/src/nsStyledElement.h
@@ -36,21 +36,11 @@ class nsStyledElementNotElementCSSInlineStyle : public nsStyledElementBase
 
 public:
   // nsIContent interface methods
-  virtual nsIAtom* GetClassAttributeName() const MOZ_OVERRIDE;
-  virtual nsIAtom* GetIDAttributeName() const MOZ_OVERRIDE;
-  virtual nsIAtom* DoGetID() const MOZ_OVERRIDE;
-  virtual const nsAttrValue* DoGetClasses() const MOZ_OVERRIDE;
-
   virtual mozilla::css::StyleRule* GetInlineStyleRule();
   virtual nsresult SetInlineStyleRule(mozilla::css::StyleRule* aStyleRule,
                                       const nsAString* aSerialized,
                                       bool aNotify) MOZ_OVERRIDE;
 
-  virtual nsresult UnsetAttr(int32_t aNameSpaceID, nsIAtom* aAttribute,
-                             bool aNotify) MOZ_OVERRIDE;
-  virtual nsresult AfterSetAttr(int32_t aNameSpaceID, nsIAtom* aAttribute,
-                                const nsAttrValue* aValue, bool aNotify) MOZ_OVERRIDE;
-
   nsICSSDeclaration* Style();
 
 protected:
diff --git a/content/base/test/test_classList.html b/content/base/test/test_classList.html
index 981c5dec78dd..3b659586be2a 100644
--- a/content/base/test/test_classList.html
+++ b/content/base/test/test_classList.html
@@ -412,16 +412,13 @@
 content.appendChild(mathMLNode);
 testClassList(mathMLNode);
 
-// Nodes not meant to be styled have a null classList property.
-
 var xmlNode = document.createElementNS(null, "foo");
 content.appendChild(xmlNode);
-is(xmlNode.classList, null, "classList is not null for plain XML nodes");
+testClassList(xmlNode);
 
 var fooNode = document.createElementNS("http://example.org/foo", "foo");
 content.appendChild(fooNode);
-is(fooNode.classList, null, "classList is not null for nodes in " +
-                            " http://example.org/foo namespace");
+testClassList(fooNode);
 
 </script>
 </pre>
diff --git a/content/html/content/src/nsGenericHTMLElement.h b/content/html/content/src/nsGenericHTMLElement.h
index 92a7d9d944da..273863ad5670 100644
--- a/content/html/content/src/nsGenericHTMLElement.h
+++ b/content/html/content/src/nsGenericHTMLElement.h
@@ -255,14 +255,6 @@ class nsGenericHTMLElement : public nsGenericHTMLElementBase,
 #undef ERROR_EVENT
 #undef FORWARDED_EVENT
 #undef EVENT
-  void GetClassName(mozilla::dom::DOMString& aClassName)
-  {
-    GetAttr(kNameSpaceID_None, nsGkAtoms::_class, aClassName);
-  }
-  void SetClassName(const nsAString& aClassName)
-  {
-    SetAttr(kNameSpaceID_None, nsGkAtoms::_class, aClassName, true);
-  }
   mozilla::dom::Element* GetOffsetParent()
   {
     mozilla::CSSIntRect rcFrame;
@@ -321,14 +313,6 @@ class nsGenericHTMLElement : public nsGenericHTMLElementBase,
 
   NS_FORWARD_NSIDOMELEMENT_TO_GENERIC
 
-  NS_IMETHOD GetId(nsAString& aId) MOZ_FINAL {
-    mozilla::dom::Element::GetId(aId);
-    return NS_OK;
-  }
-  NS_IMETHOD SetId(const nsAString& aId) MOZ_FINAL {
-    mozilla::dom::Element::SetId(aId);
-    return NS_OK;
-  }
   NS_IMETHOD GetTitle(nsAString& aTitle) MOZ_FINAL {
     nsString title;
     GetTitle(title);
diff --git a/content/html/document/src/ImageDocument.cpp b/content/html/document/src/ImageDocument.cpp
index f8f57f5ddc98..0a60f8d72b55 100644
--- a/content/html/document/src/ImageDocument.cpp
+++ b/content/html/document/src/ImageDocument.cpp
@@ -459,7 +459,7 @@ ImageDocument::Notify(imgIRequest* aRequest, int32_t aType, const nsIntRect* aDa
     return OnStartContainer(aRequest, image);
   }
 
-  nsDOMTokenList* classList = mImageContent->AsElement()->GetClassList();
+  nsDOMTokenList* classList = mImageContent->AsElement()->ClassList();
   mozilla::ErrorResult rv;
   if (aType == imgINotificationObserver::DECODE_COMPLETE) {
     if (mImageContent && !nsContentUtils::IsChildOfSameType(this)) {
@@ -494,7 +494,7 @@ ImageDocument::Notify(imgIRequest* aRequest, int32_t aType, const nsIntRect* aDa
 void
 ImageDocument::SetModeClass(eModeClasses mode)
 {
-  nsDOMTokenList* classList = mImageContent->AsElement()->GetClassList();
+  nsDOMTokenList* classList = mImageContent->AsElement()->ClassList();
   mozilla::ErrorResult rv;
 
   if (mode == eShrinkToFit) {
diff --git a/content/mathml/content/src/nsMathMLElementFactory.cpp b/content/mathml/content/src/nsMathMLElementFactory.cpp
index e4fec647263b..4b4c978b6d4c 100644
--- a/content/mathml/content/src/nsMathMLElementFactory.cpp
+++ b/content/mathml/content/src/nsMathMLElementFactory.cpp
@@ -13,11 +13,6 @@ using namespace mozilla::dom;
 nsresult
 NS_NewMathMLElement(Element** aResult, already_AddRefed<nsINodeInfo>&& aNodeInfo)
 {
-  nsCOMPtr<nsINodeInfo> ni = aNodeInfo;
-  ni->SetIDAttributeAtom(nsGkAtoms::id);
-
-  nsMathMLElement* it = new nsMathMLElement(ni.forget());
-
-  NS_ADDREF(*aResult = it);
+  NS_ADDREF(*aResult = new nsMathMLElement(aNodeInfo));
   return NS_OK;
 }
diff --git a/content/svg/content/src/nsSVGElement.cpp b/content/svg/content/src/nsSVGElement.cpp
index 23e923230c59..eaeddd37c48d 100644
--- a/content/svg/content/src/nsSVGElement.cpp
+++ b/content/svg/content/src/nsSVGElement.cpp
@@ -99,7 +99,7 @@ nsSVGElement::WrapNode(JSContext *aCx)
 
 /* readonly attribute SVGAnimatedString className; */
 NS_IMETHODIMP
-nsSVGElement::GetClassName(nsISupports** aClassName)
+nsSVGElement::GetSVGClassName(nsISupports** aClassName)
 {
   *aClassName = ClassName().take();
   return NS_OK;
@@ -240,15 +240,6 @@ NS_IMPL_ISUPPORTS_INHERITED(nsSVGElement, nsSVGElementBase,
 //----------------------------------------------------------------------
 // nsIContent methods
 
-const nsAttrValue*
-nsSVGElement::DoGetClasses() const
-{
-  if (mClassAttribute.IsAnimated()) {
-    return mClassAnimAttr;
-  }
-  return nsSVGElementBase::DoGetClasses();
-}
-
 nsresult
 nsSVGElement::BindToTree(nsIDocument* aDocument, nsIContent* aParent,
                          nsIContent* aBindingParent,
@@ -1095,19 +1086,6 @@ nsSVGElement::sMaskMap[] = {
 //----------------------------------------------------------------------
 // nsIDOMSVGElement methods
 
-/* attribute DOMString id; */
-NS_IMETHODIMP nsSVGElement::GetId(nsAString & aId)
-{
-  GetAttr(kNameSpaceID_None, nsGkAtoms::id, aId);
-
-  return NS_OK;
-}
-
-NS_IMETHODIMP nsSVGElement::SetId(const nsAString & aId)
-{
-  return SetAttr(kNameSpaceID_None, nsGkAtoms::id, aId, true);
-}
-
 /* readonly attribute nsIDOMSVGSVGElement ownerSVGElement; */
 NS_IMETHODIMP
 nsSVGElement::GetOwnerSVGElement(nsIDOMSVGElement * *aOwnerSVGElement)
diff --git a/content/svg/content/src/nsSVGElement.h b/content/svg/content/src/nsSVGElement.h
index bc72a134db8a..88c4430640aa 100644
--- a/content/svg/content/src/nsSVGElement.h
+++ b/content/svg/content/src/nsSVGElement.h
@@ -96,7 +96,6 @@ class nsSVGElement : public nsSVGElementBase    // nsIContent
   // nsISupports
   NS_DECL_ISUPPORTS_INHERITED
 
-  virtual const nsAttrValue* DoGetClasses() const MOZ_OVERRIDE;
   void DidAnimateClass();
 
   // nsIContent interface methods
@@ -305,6 +304,13 @@ class nsSVGElement : public nsSVGElementBase    // nsIContent
   virtual nsIAtom* GetTransformListAttrName() const {
     return nullptr;
   }
+  const nsAttrValue* GetAnimatedClassName() const
+  {
+    if (!mClassAttribute.IsAnimated()) {
+      return nullptr;
+    }
+    return mClassAnimAttr;
+  }
 
   virtual nsIDOMNode* AsDOMNode() MOZ_FINAL MOZ_OVERRIDE { return this; }
   virtual bool IsTransformable() { return false; }
diff --git a/content/xml/content/src/nsXMLElement.cpp b/content/xml/content/src/nsXMLElement.cpp
index 1fa15a97e3f8..1ef2fe9366ed 100644
--- a/content/xml/content/src/nsXMLElement.cpp
+++ b/content/xml/content/src/nsXMLElement.cpp
@@ -29,107 +29,3 @@ nsXMLElement::WrapNode(JSContext *aCx)
 }
 
 NS_IMPL_ELEMENT_CLONE(nsXMLElement)
-
-nsresult
-nsXMLElement::UnsetAttr(int32_t aNameSpaceID, nsIAtom* aAttribute,
-                        bool aNotify)
-{
-  nsAutoScriptBlocker scriptBlocker;
-  bool isId = false;
-  if (aAttribute == GetIDAttributeName() &&
-      aNameSpaceID == kNameSpaceID_None) {
-    // Have to do this before clearing flag. See RemoveFromIdTable
-    RemoveFromIdTable();
-    isId = true;
-  }
-
-  nsMutationGuard guard;
-
-  nsresult rv = Element::UnsetAttr(aNameSpaceID, aAttribute, aNotify);
-
-  if (isId &&
-      (!guard.Mutated(0) ||
-       !mNodeInfo->GetIDAttributeAtom() ||
-       !HasAttr(kNameSpaceID_None, GetIDAttributeName()))) {
-    ClearHasID();
-  }
-  
-  return rv;
-}
-
-nsIAtom *
-nsXMLElement::GetIDAttributeName() const
-{
-  return mNodeInfo->GetIDAttributeAtom();
-}
-
-nsIAtom*
-nsXMLElement::DoGetID() const
-{
-  NS_ASSERTION(HasID(), "Unexpected call");
-
-  const nsAttrValue* attrVal = mAttrsAndChildren.GetAttr(GetIDAttributeName());
-  return attrVal ? attrVal->GetAtomValue() : nullptr;
-}
-
-void
-nsXMLElement::NodeInfoChanged(nsINodeInfo* aOldNodeInfo)
-{
-  NS_ASSERTION(!IsInDoc() ||
-               aOldNodeInfo->GetDocument() == mNodeInfo->GetDocument(),
-               "Can only change document if we're not inside one");
-  nsIDocument* doc = GetCurrentDoc();
-
-  if (HasID() && doc) {
-    const nsAttrValue* attrVal =
-      mAttrsAndChildren.GetAttr(aOldNodeInfo->GetIDAttributeAtom());
-    if (attrVal) {
-      RemoveFromIdTable(attrVal->GetAtomValue());
-    }
-  }
-  
-  ClearHasID();
-
-  nsIAtom* IDName = GetIDAttributeName();
-  if (IDName) {
-    const nsAttrValue* attrVal = mAttrsAndChildren.GetAttr(IDName);
-    if (attrVal) {
-      SetHasID();
-      if (attrVal->Type() == nsAttrValue::eString) {
-        nsString idVal(attrVal->GetStringValue());
-
-        // Create an atom from the value and set it into the attribute list. 
-        const_cast<nsAttrValue*>(attrVal)->ParseAtom(idVal);
-      }
-      NS_ASSERTION(attrVal->Type() == nsAttrValue::eAtom,
-                   "Should be atom by now");
-      if (doc) {
-        AddToIdTable(attrVal->GetAtomValue());
-      }
-    }
-  }
-}
-
-bool
-nsXMLElement::ParseAttribute(int32_t aNamespaceID,
-                             nsIAtom* aAttribute,
-                             const nsAString& aValue,
-                             nsAttrValue& aResult)
-{
-  if (aAttribute == GetIDAttributeName() &&
-      aNamespaceID == kNameSpaceID_None) {
-    // Store id as an atom.  id="" means that the element has no id,
-    // not that it has an emptystring as the id.
-    RemoveFromIdTable();
-    if (aValue.IsEmpty()) {
-      ClearHasID();
-      return false;
-    }
-    aResult.ParseAtom(aValue);
-    SetHasID();
-    AddToIdTable(aResult.GetAtomValue());
-    return true;
-  }
-
-  return false;
-}
diff --git a/content/xml/content/src/nsXMLElement.h b/content/xml/content/src/nsXMLElement.h
index da7d789d9dac..ebfb4a8780b6 100644
--- a/content/xml/content/src/nsXMLElement.h
+++ b/content/xml/content/src/nsXMLElement.h
@@ -34,19 +34,6 @@ class nsXMLElement : public mozilla::dom::Element,
 
   virtual nsIDOMNode* AsDOMNode() MOZ_OVERRIDE { return this; }
 
-  // nsIContent interface methods
-  virtual nsIAtom *GetIDAttributeName() const MOZ_OVERRIDE;
-  virtual nsIAtom* DoGetID() const MOZ_OVERRIDE;
-  virtual nsresult UnsetAttr(int32_t aNameSpaceID, nsIAtom* aAttribute,
-                             bool aNotify) MOZ_OVERRIDE;
-  virtual bool ParseAttribute(int32_t aNamespaceID,
-                                nsIAtom* aAttribute,
-                                const nsAString& aValue,
-                                nsAttrValue& aResult) MOZ_OVERRIDE;
-
-  // Element overrides
-  virtual void NodeInfoChanged(nsINodeInfo* aOldNodeInfo) MOZ_OVERRIDE;
-
 protected:
   virtual JSObject* WrapNode(JSContext *aCx) MOZ_OVERRIDE;
 };
diff --git a/content/xml/document/src/nsXMLContentSink.cpp b/content/xml/document/src/nsXMLContentSink.cpp
index d21971d8c0f7..db85b3fb1da0 100644
--- a/content/xml/document/src/nsXMLContentSink.cpp
+++ b/content/xml/document/src/nsXMLContentSink.cpp
@@ -937,10 +937,9 @@ NS_IMETHODIMP
 nsXMLContentSink::HandleStartElement(const char16_t *aName,
                                      const char16_t **aAtts,
                                      uint32_t aAttsCount,
-                                     int32_t aIndex,
                                      uint32_t aLineNumber)
 {
-  return HandleStartElement(aName, aAtts, aAttsCount, aIndex, aLineNumber,
+  return HandleStartElement(aName, aAtts, aAttsCount, aLineNumber,
                             true);
 }
 
@@ -948,11 +947,9 @@ nsresult
 nsXMLContentSink::HandleStartElement(const char16_t *aName,
                                      const char16_t **aAtts,
                                      uint32_t aAttsCount,
-                                     int32_t aIndex,
                                      uint32_t aLineNumber,
                                      bool aInterruptable)
 {
-  NS_PRECONDITION(aIndex >= -1, "Bogus aIndex");
   NS_PRECONDITION(aAttsCount % 2 == 0, "incorrect aAttsCount");
   // Adjust aAttsCount so it's the actual number of attributes
   aAttsCount /= 2;
@@ -998,17 +995,6 @@ nsXMLContentSink::HandleStartElement(const char16_t *aName,
   result = PushContent(content);
   NS_ENSURE_SUCCESS(result, result);
 
-  // Set the ID attribute atom on the node info object for this node
-  // This must occur before the attributes are added so the name
-  // of the id attribute is known.
-  if (aIndex != -1 && NS_SUCCEEDED(result)) {
-    nsCOMPtr<nsIAtom> IDAttr = do_GetAtom(aAtts[aIndex]);
-
-    if (IDAttr) {
-      nodeInfo->SetIDAttributeAtom(IDAttr);
-    }
-  }
-
   // Set the attributes on the new content element
   result = AddAttributes(aAtts, content);
 
@@ -1384,7 +1370,7 @@ nsXMLContentSink::ReportError(const char16_t* aErrorText,
   parsererror.Append((char16_t)0xFFFF);
   parsererror.AppendLiteral("parsererror");
   
-  rv = HandleStartElement(parsererror.get(), noAtts, 0, -1, (uint32_t)-1,
+  rv = HandleStartElement(parsererror.get(), noAtts, 0, (uint32_t)-1,
                           false);
   NS_ENSURE_SUCCESS(rv, rv);
 
@@ -1395,7 +1381,7 @@ nsXMLContentSink::ReportError(const char16_t* aErrorText,
   sourcetext.Append((char16_t)0xFFFF);
   sourcetext.AppendLiteral("sourcetext");
 
-  rv = HandleStartElement(sourcetext.get(), noAtts, 0, -1, (uint32_t)-1,
+  rv = HandleStartElement(sourcetext.get(), noAtts, 0, (uint32_t)-1,
                           false);
   NS_ENSURE_SUCCESS(rv, rv);
   
diff --git a/content/xml/document/src/nsXMLContentSink.h b/content/xml/document/src/nsXMLContentSink.h
index 126ad168199c..a5c5e45f00e0 100644
--- a/content/xml/document/src/nsXMLContentSink.h
+++ b/content/xml/document/src/nsXMLContentSink.h
@@ -157,8 +157,7 @@ class nsXMLContentSink : public nsContentSink,
   bool IsMonolithicContainer(nsINodeInfo* aNodeInfo);
 
   nsresult HandleStartElement(const char16_t *aName, const char16_t **aAtts, 
-                              uint32_t aAttsCount, int32_t aIndex, 
-                              uint32_t aLineNumber,
+                              uint32_t aAttsCount, uint32_t aLineNumber,
                               bool aInterruptable);
   nsresult HandleEndElement(const char16_t *aName, bool aInterruptable);
   nsresult HandleCharacterData(const char16_t *aData, uint32_t aLength,
diff --git a/content/xul/content/src/nsXULElement.cpp b/content/xul/content/src/nsXULElement.cpp
index c1eac141beeb..79b0aa14d301 100644
--- a/content/xul/content/src/nsXULElement.cpp
+++ b/content/xul/content/src/nsXULElement.cpp
@@ -336,6 +336,12 @@ NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INHERITED(nsXULElement,
     }
 NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
 
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN_INHERITED(nsXULElement,
+                                                nsStyledElement)
+    // Why aren't we unlinking the prototype?
+    tmp->ClearHasID();
+NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+
 NS_IMPL_ADDREF_INHERITED(nsXULElement, nsStyledElement)
 NS_IMPL_RELEASE_INHERITED(nsXULElement, nsStyledElement)
 
@@ -1503,7 +1509,6 @@ nsXULElement::GetBoxObject(ErrorResult& rv)
   }
 
 
-NS_IMPL_XUL_STRING_ATTR(ClassName, _class)
 NS_IMPL_XUL_STRING_ATTR(Align, align)
 NS_IMPL_XUL_STRING_ATTR(Dir, dir)
 NS_IMPL_XUL_STRING_ATTR(Flex, flex)
diff --git a/content/xul/content/src/nsXULElement.h b/content/xul/content/src/nsXULElement.h
index 62307e1cda68..e506899e7898 100644
--- a/content/xul/content/src/nsXULElement.h
+++ b/content/xul/content/src/nsXULElement.h
@@ -379,8 +379,7 @@ class nsXULElement MOZ_FINAL : public nsStyledElement,
 
     // nsISupports
     NS_DECL_ISUPPORTS_INHERITED
-    NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED_NO_UNLINK(nsXULElement,
-                                                       mozilla::dom::Element)
+    NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(nsXULElement, nsStyledElement)
 
     // nsINode
     virtual nsresult PreHandleEvent(
diff --git a/content/xul/document/src/XULDocument.cpp b/content/xul/document/src/XULDocument.cpp
index b6b882bd03e0..0b1aec6cfd3c 100644
--- a/content/xul/document/src/XULDocument.cpp
+++ b/content/xul/document/src/XULDocument.cpp
@@ -966,8 +966,7 @@ XULDocument::AttributeWillChange(nsIDocument* aDocument,
 
     // XXXbz check aNameSpaceID, dammit!
     // See if we need to update our ref map.
-    if (aAttribute == nsGkAtoms::ref ||
-        (aAttribute == nsGkAtoms::id && !aElement->GetIDAttributeName())) {
+    if (aAttribute == nsGkAtoms::ref) {
         // Might not need this, but be safe for now.
         nsCOMPtr<nsIMutationObserver> kungFuDeathGrip(this);
         RemoveElementFromRefMap(aElement);
@@ -986,8 +985,7 @@ XULDocument::AttributeChanged(nsIDocument* aDocument,
 
     // XXXbz check aNameSpaceID, dammit!
     // See if we need to update our ref map.
-    if (aAttribute == nsGkAtoms::ref ||
-        (aAttribute == nsGkAtoms::id && !aElement->GetIDAttributeName())) {
+    if (aAttribute == nsGkAtoms::ref) {
         AddElementToRefMap(aElement);
     }
     
@@ -1927,9 +1925,6 @@ static void
 GetRefMapAttribute(Element* aElement, nsAutoString* aValue)
 {
     aElement->GetAttr(kNameSpaceID_None, nsGkAtoms::ref, *aValue);
-    if (aValue->IsEmpty() && !aElement->GetIDAttributeName()) {
-        aElement->GetAttr(kNameSpaceID_None, nsGkAtoms::id, *aValue);
-    }
 }
 
 nsresult
diff --git a/content/xul/document/src/nsXULContentSink.cpp b/content/xul/document/src/nsXULContentSink.cpp
index 804a38a5c4cd..fc68b984c0c1 100644
--- a/content/xul/document/src/nsXULContentSink.cpp
+++ b/content/xul/document/src/nsXULContentSink.cpp
@@ -456,13 +456,11 @@ NS_IMETHODIMP
 XULContentSinkImpl::HandleStartElement(const char16_t *aName, 
                                        const char16_t **aAtts,
                                        uint32_t aAttsCount, 
-                                       int32_t aIndex, 
                                        uint32_t aLineNumber)
 { 
   // XXX Hopefully the parser will flag this before we get here. If
   // we're in the epilog, there should be no new elements
   NS_PRECONDITION(mState != eInEpilog, "tag in XUL doc epilog");
-  NS_PRECONDITION(aIndex >= -1, "Bogus aIndex");
   NS_PRECONDITION(aAttsCount % 2 == 0, "incorrect aAttsCount");
   // Adjust aAttsCount so it's the actual number of attributes
   aAttsCount /= 2;
@@ -503,15 +501,6 @@ XULContentSinkImpl::HandleStartElement(const char16_t *aName,
       break;
   }
 
-  // Set the ID attribute atom on the node info object for this node
-  if (aIndex != -1 && NS_SUCCEEDED(rv)) {
-    nsCOMPtr<nsIAtom> IDAttr = do_GetAtom(aAtts[aIndex]);
-
-    if (IDAttr) {
-      nodeInfo->SetIDAttributeAtom(IDAttr);
-    }
-  }
-
   return rv;
 }
 
@@ -721,7 +710,7 @@ XULContentSinkImpl::ReportError(const char16_t* aErrorText,
   parsererror.Append((char16_t)0xFFFF);
   parsererror.AppendLiteral("parsererror");
   
-  rv = HandleStartElement(parsererror.get(), noAtts, 0, -1, 0);
+  rv = HandleStartElement(parsererror.get(), noAtts, 0, 0);
   NS_ENSURE_SUCCESS(rv,rv);
 
   rv = HandleCharacterData(aErrorText, NS_strlen(aErrorText));
@@ -731,7 +720,7 @@ XULContentSinkImpl::ReportError(const char16_t* aErrorText,
   sourcetext.Append((char16_t)0xFFFF);
   sourcetext.AppendLiteral("sourcetext");
 
-  rv = HandleStartElement(sourcetext.get(), noAtts, 0, -1, 0);
+  rv = HandleStartElement(sourcetext.get(), noAtts, 0, 0);
   NS_ENSURE_SUCCESS(rv,rv);
   
   rv = HandleCharacterData(aSourceText, NS_strlen(aSourceText));
diff --git a/dom/imptests/failures/html/dom/nodes/test_Node-properties.html.json b/dom/imptests/failures/html/dom/nodes/test_Node-properties.html.json
index 2f99d6512b8c..8c7b35264d9f 100644
--- a/dom/imptests/failures/html/dom/nodes/test_Node-properties.html.json
+++ b/dom/imptests/failures/html/dom/nodes/test_Node-properties.html.json
@@ -3,7 +3,5 @@
   "foreignDoc.characterSet": true,
   "xmlDoc.characterSet": true,
   "xmlElement.namespaceURI": true,
-  "xmlElement.className": true,
-  "detachedXmlElement.namespaceURI": true,
-  "detachedXmlElement.className": true
+  "detachedXmlElement.namespaceURI": true
 }
diff --git a/dom/imptests/failures/html/dom/test_interfaces.html.json b/dom/imptests/failures/html/dom/test_interfaces.html.json
index cf7880ee4086..830faf148b3b 100644
--- a/dom/imptests/failures/html/dom/test_interfaces.html.json
+++ b/dom/imptests/failures/html/dom/test_interfaces.html.json
@@ -35,13 +35,11 @@
   "Element interface: attribute namespaceURI": true,
   "Element interface: attribute prefix": true,
   "Element interface: attribute localName": true,
-  "Element interface: attribute className": true,
   "Element interface: operation prepend([object Object],[object Object])": true,
   "Element interface: operation append([object Object],[object Object])": true,
   "Element interface: operation before([object Object],[object Object])": true,
   "Element interface: operation after([object Object],[object Object])": true,
   "Element interface: operation replace([object Object],[object Object])": true,
-  "Element interface: element must inherit property \"className\" with the proper type (5)": true,
   "Element interface: element must inherit property \"prepend\" with the proper type (23)": true,
   "Element interface: calling prepend([object Object],[object Object]) on element with too few arguments must throw TypeError": true,
   "Element interface: element must inherit property \"append\" with the proper type (24)": true,
diff --git a/dom/interfaces/core/nsIDOMElement.idl b/dom/interfaces/core/nsIDOMElement.idl
index 08f8c966654b..7bbc73c1e4b7 100644
--- a/dom/interfaces/core/nsIDOMElement.idl
+++ b/dom/interfaces/core/nsIDOMElement.idl
@@ -20,6 +20,8 @@ interface nsIDOMElement : nsIDOMNode
 {
   readonly attribute DOMString        tagName;
 
+           attribute DOMString        id;
+           attribute DOMString        className;
   /**
    * Returns a DOMTokenList object reflecting the class attribute.
    */
diff --git a/dom/interfaces/html/nsIDOMHTMLElement.idl b/dom/interfaces/html/nsIDOMHTMLElement.idl
index 8badbe446c16..f2caf94ef9e0 100644
--- a/dom/interfaces/html/nsIDOMHTMLElement.idl
+++ b/dom/interfaces/html/nsIDOMHTMLElement.idl
@@ -23,12 +23,9 @@ interface nsIDOMHTMLMenuElement;
 interface nsIDOMHTMLElement : nsIDOMElement
 {
   // metadata attributes
-           attribute DOMString        id;
            attribute DOMString        title;
            attribute DOMString        lang;
            attribute DOMString        dir;
-  [binaryname(DOMClassName)]
-           attribute DOMString        className;
   readonly attribute nsISupports      dataset;
 
            attribute boolean                        itemScope;
diff --git a/dom/interfaces/svg/nsIDOMSVGElement.idl b/dom/interfaces/svg/nsIDOMSVGElement.idl
index 0c740ddccc41..5cb7fa6608d1 100644
--- a/dom/interfaces/svg/nsIDOMSVGElement.idl
+++ b/dom/interfaces/svg/nsIDOMSVGElement.idl
@@ -12,11 +12,11 @@ interface nsIDOMCSSValue;
 [uuid(abdf347a-0063-42cc-b6fc-c9a19a65248e)]
 interface nsIDOMSVGElement : nsIDOMElement
 {
-  attribute DOMString id;
             // raises DOMException on setting
   readonly attribute nsIDOMSVGElement    ownerSVGElement;
   readonly attribute nsIDOMSVGElement    viewportElement;
 
+  [binaryname(SVGClassName)]
   readonly attribute nsISupports   className;
   readonly attribute nsIDOMCSSStyleDeclaration style;
 };
diff --git a/dom/interfaces/xul/nsIDOMXULElement.idl b/dom/interfaces/xul/nsIDOMXULElement.idl
index 86a8acc25726..16d516fd4da0 100644
--- a/dom/interfaces/xul/nsIDOMXULElement.idl
+++ b/dom/interfaces/xul/nsIDOMXULElement.idl
@@ -15,8 +15,6 @@ interface nsIBoxObject;
 [uuid(e89578c8-64ec-4047-984a-cce1b1735543)]
 interface nsIDOMXULElement : nsIDOMElement
 {
-  attribute DOMString                 className;
-
   // Layout properties
   attribute DOMString align;
   attribute DOMString dir;
diff --git a/dom/smil/test/test_smilValues.xhtml b/dom/smil/test/test_smilValues.xhtml
index a656e08dc9cb..37a4a05cb509 100644
--- a/dom/smil/test/test_smilValues.xhtml
+++ b/dom/smil/test/test_smilValues.xhtml
@@ -159,6 +159,7 @@ function checkSample(anim, expectedValue, sampleTime, caseNum)
     " (values: '" + anim.getAttribute('values') + "')," +
     "t=" + sampleTime +
     ": Unexpected sample value:";
+  is(typeof anim.targetElement.className, "object");
   is(anim.targetElement.className.animVal, expectedValue, msg);
 }
 
diff --git a/dom/webidl/Element.webidl b/dom/webidl/Element.webidl
index 005207aa3114..d48af43acfca 100644
--- a/dom/webidl/Element.webidl
+++ b/dom/webidl/Element.webidl
@@ -28,12 +28,10 @@ interface Element : Node {
 
   [Pure]
            attribute DOMString id;
-/*
-  FIXME Bug 810677 Move className from HTMLElement to Element
+  [Pure]
            attribute DOMString className;
-*/
   [Constant]
-  readonly attribute DOMTokenList? classList;
+  readonly attribute DOMTokenList classList;
 
   [SameObject]
   readonly attribute MozNamedAttrMap attributes;
diff --git a/dom/xbl/nsXBLContentSink.cpp b/dom/xbl/nsXBLContentSink.cpp
index b285332f197c..61eac4fbce31 100644
--- a/dom/xbl/nsXBLContentSink.cpp
+++ b/dom/xbl/nsXBLContentSink.cpp
@@ -251,10 +251,10 @@ NS_IMETHODIMP
 nsXBLContentSink::HandleStartElement(const char16_t *aName, 
                                      const char16_t **aAtts, 
                                      uint32_t aAttsCount, 
-                                     int32_t aIndex, 
                                      uint32_t aLineNumber)
 {
-  nsresult rv = nsXMLContentSink::HandleStartElement(aName,aAtts,aAttsCount,aIndex,aLineNumber);
+  nsresult rv = nsXMLContentSink::HandleStartElement(aName, aAtts, aAttsCount,
+                                                     aLineNumber);
   if (NS_FAILED(rv))
     return rv;
 
diff --git a/dom/xbl/nsXBLContentSink.h b/dom/xbl/nsXBLContentSink.h
index 37d46fadadc5..30419ff17c8c 100644
--- a/dom/xbl/nsXBLContentSink.h
+++ b/dom/xbl/nsXBLContentSink.h
@@ -69,7 +69,6 @@ class nsXBLContentSink : public nsXMLContentSink {
   NS_IMETHOD HandleStartElement(const char16_t *aName, 
                                 const char16_t **aAtts, 
                                 uint32_t aAttsCount, 
-                                int32_t aIndex, 
                                 uint32_t aLineNumber) MOZ_OVERRIDE;
 
   NS_IMETHOD HandleEndElement(const char16_t *aName) MOZ_OVERRIDE;
diff --git a/dom/xslt/xslt/txMozillaStylesheetCompiler.cpp b/dom/xslt/xslt/txMozillaStylesheetCompiler.cpp
index 18a3eb522da9..9ce956d8d3b5 100644
--- a/dom/xslt/xslt/txMozillaStylesheetCompiler.cpp
+++ b/dom/xslt/xslt/txMozillaStylesheetCompiler.cpp
@@ -118,13 +118,12 @@ NS_IMETHODIMP
 txStylesheetSink::HandleStartElement(const char16_t *aName,
                                      const char16_t **aAtts,
                                      uint32_t aAttsCount,
-                                     int32_t aIndex,
                                      uint32_t aLineNumber)
 {
     NS_PRECONDITION(aAttsCount % 2 == 0, "incorrect aAttsCount");
 
     nsresult rv =
-        mCompiler->startElement(aName, aAtts, aAttsCount / 2, aIndex);
+        mCompiler->startElement(aName, aAtts, aAttsCount / 2);
     if (NS_FAILED(rv)) {
         mCompiler->cancel(rv);
 
diff --git a/dom/xslt/xslt/txStylesheetCompiler.cpp b/dom/xslt/xslt/txStylesheetCompiler.cpp
index b53e9ee0d533..6535ea38b6d2 100644
--- a/dom/xslt/xslt/txStylesheetCompiler.cpp
+++ b/dom/xslt/xslt/txStylesheetCompiler.cpp
@@ -103,7 +103,7 @@ txStylesheetCompiler::startElement(int32_t aNamespaceID, nsIAtom* aLocalName,
 nsresult
 txStylesheetCompiler::startElement(const char16_t *aName,
                                    const char16_t **aAttrs,
-                                   int32_t aAttrCount, int32_t aIDOffset)
+                                   int32_t aAttrCount)
 {
     if (NS_FAILED(mStatus)) {
         // ignore content after failure
@@ -162,12 +162,8 @@ txStylesheetCompiler::startElement(const char16_t *aName,
                                   getter_AddRefs(localname), &namespaceID);
     NS_ENSURE_SUCCESS(rv, rv);
 
-    int32_t idOffset = aIDOffset;
-    if (idOffset > 0) {
-        idOffset /= 2;
-    }
     return startElementInternal(namespaceID, localname, prefix, atts,
-                                aAttrCount, idOffset);
+                                aAttrCount);
 }
 
 nsresult
@@ -175,8 +171,7 @@ txStylesheetCompiler::startElementInternal(int32_t aNamespaceID,
                                            nsIAtom* aLocalName,
                                            nsIAtom* aPrefix,
                                            txStylesheetAttr* aAttributes,
-                                           int32_t aAttrCount,
-                                           int32_t aIDOffset)
+                                           int32_t aAttrCount)
 {
     nsresult rv = NS_OK;
     int32_t i;
@@ -188,6 +183,16 @@ txStylesheetCompiler::startElementInternal(int32_t aNamespaceID,
     for (i = 0; i < aAttrCount; ++i) {
         txStylesheetAttr* attr = aAttributes + i;
 
+        // id
+        if (mEmbedStatus == eNeedEmbed &&
+            attr->mLocalName == nsGkAtoms::id &&
+            attr->mNamespaceID == kNameSpaceID_None &&
+            attr->mValue.Equals(mTarget)) {
+            // We found the right ID, signal to compile the
+            // embedded stylesheet.
+            mEmbedStatus = eInEmbed;
+        }
+
         // xml:space
         if (attr->mNamespaceID == kNameSpaceID_XML &&
             attr->mLocalName == nsGkAtoms::space) {
@@ -277,14 +282,6 @@ txStylesheetCompiler::startElementInternal(int32_t aNamespaceID,
         }
     }
 
-    if (mEmbedStatus == eNeedEmbed) {
-        // handle embedded stylesheets
-        if (aIDOffset >= 0 && aAttributes[aIDOffset].mValue.Equals(mTarget)) {
-            // We found the right ID, signal to compile the 
-            // embedded stylesheet.
-            mEmbedStatus = eInEmbed;
-        }
-    }
     const txElementHandler* handler;
     do {
         handler = isInstruction ?
diff --git a/dom/xslt/xslt/txStylesheetCompiler.h b/dom/xslt/xslt/txStylesheetCompiler.h
index ac385e6b24aa..aa7d6cce6b7b 100644
--- a/dom/xslt/xslt/txStylesheetCompiler.h
+++ b/dom/xslt/xslt/txStylesheetCompiler.h
@@ -202,7 +202,7 @@ class txStylesheetCompiler MOZ_FINAL : private txStylesheetCompilerState,
                           int32_t aAttrCount);
     nsresult startElement(const char16_t *aName,
                           const char16_t **aAtts,
-                          int32_t aAttrCount, int32_t aIDOffset);
+                          int32_t aAttrCount);
     nsresult endElement();
     nsresult characters(const nsAString& aStr);
     nsresult doneLoading();
@@ -224,8 +224,7 @@ class txStylesheetCompiler MOZ_FINAL : private txStylesheetCompilerState,
     nsresult startElementInternal(int32_t aNamespaceID, nsIAtom* aLocalName,
                                   nsIAtom* aPrefix,
                                   txStylesheetAttr* aAttributes,
-                                  int32_t aAttrCount,
-                                  int32_t aIDOffset = -1);
+                                  int32_t aAttrCount);
 
     nsresult flushCharacters();
     nsresult ensureNewElementContext();
diff --git a/layout/reftests/bugs/495354-1a.xhtml b/layout/reftests/bugs/495354-1a.xhtml
index 085754d06f1e..cc5bb9423e5b 100644
--- a/layout/reftests/bugs/495354-1a.xhtml
+++ b/layout/reftests/bugs/495354-1a.xhtml
@@ -2,7 +2,7 @@
 <head>
 <bindings xmlns="http://www.mozilla.org/xbl"><binding id="x"><content><caption xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"><children xmlns="http://www.mozilla.org/xbl"/></caption></content></binding></bindings>
 </head>
-<body onload="document.getElementById('x').innerHTML = '9';">
-<span id="x" style="-moz-binding: url(#x)"><div>123</div></span>
+<body onload="document.getElementById('y').innerHTML = '9';">
+<span id="y" style="-moz-binding: url(#x)"><div>123</div></span>
 </body>
 </html>
diff --git a/layout/reftests/bugs/495354-1b.xhtml b/layout/reftests/bugs/495354-1b.xhtml
index f0ff0c929e80..0d7a14bd40c1 100644
--- a/layout/reftests/bugs/495354-1b.xhtml
+++ b/layout/reftests/bugs/495354-1b.xhtml
@@ -2,7 +2,7 @@
 <head>
 <bindings xmlns="http://www.mozilla.org/xbl"><binding id="x"><content><caption xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"><children xmlns="http://www.mozilla.org/xbl"/></caption></content></binding></bindings>
 </head>
-<body onload="document.getElementById('x').innerHTML = '9';">
-<span id="x" style="-moz-binding: url(#x)"><div style="border: 5px solid green">123</div></span>
+<body onload="document.getElementById('y').innerHTML = '9';">
+<span id="y" style="-moz-binding: url(#x)"><div style="border: 5px solid green">123</div></span>
 </body>
 </html>
diff --git a/layout/style/nsCSSRuleProcessor.cpp b/layout/style/nsCSSRuleProcessor.cpp
index c65852352447..f0ab036add57 100644
--- a/layout/style/nsCSSRuleProcessor.cpp
+++ b/layout/style/nsCSSRuleProcessor.cpp
@@ -2754,7 +2754,7 @@ nsCSSRuleProcessor::HasAttributeDependentStyle(AttributeRuleProcessorData* aData
   // rules we might stop matching; if the after change notification, the
   // ones we might have started matching.
   if (cascade) {
-    if (aData->mAttribute == aData->mElement->GetIDAttributeName()) {
+    if (aData->mAttribute == nsGkAtoms::id) {
       nsIAtom* id = aData->mElement->GetID();
       if (id) {
         AtomSelectorEntry *entry =
@@ -2769,7 +2769,7 @@ nsCSSRuleProcessor::HasAttributeDependentStyle(AttributeRuleProcessorData* aData
       EnumerateSelectors(cascade->mPossiblyNegatedIDSelectors, &data);
     }
     
-    if (aData->mAttribute == aData->mElement->GetClassAttributeName()) {
+    if (aData->mAttribute == nsGkAtoms::_class) {
       const nsAttrValue* elementClasses = aData->mElement->GetClasses();
       if (elementClasses) {
         int32_t atomCount = elementClasses->GetAtomCount();
diff --git a/parser/htmlparser/public/nsIExpatSink.idl b/parser/htmlparser/public/nsIExpatSink.idl
index 74bc9c33d08a..43500b0e0118 100644
--- a/parser/htmlparser/public/nsIExpatSink.idl
+++ b/parser/htmlparser/public/nsIExpatSink.idl
@@ -27,15 +27,11 @@ interface nsIExpatSink : nsISupports
    *        and attributes that are defined to have default values in a DTD are
    *        present in aAtts.
    * @param aAttsCount the number of elements in aAtts.
-   * @param aIndex If the element has an attribute of type ID, then
-   *        aAtts[aIndex] is the name of that attribute.  Otherwise, aIndex
-   *        is -1
    * @param aLineNumber the line number of the start tag in the data stream.
    */
   void HandleStartElement(in wstring aName,
                           [array, size_is(aAttsCount)] in wstring aAtts,
                           in unsigned long aAttsCount,
-                          in long aIndex,
                           in unsigned long aLineNumber);
 
   /**
diff --git a/parser/htmlparser/src/nsExpatDriver.cpp b/parser/htmlparser/src/nsExpatDriver.cpp
index f9a013bad1e0..eb839a62fc71 100644
--- a/parser/htmlparser/src/nsExpatDriver.cpp
+++ b/parser/htmlparser/src/nsExpatDriver.cpp
@@ -381,7 +381,6 @@ nsExpatDriver::HandleStartElement(const char16_t *aValue,
   if (mSink) {
     nsresult rv = mSink->
       HandleStartElement(aValue, aAtts, attrArrayLength,
-                         XML_GetIdAttributeIndex(mExpatParser),
                          XML_GetCurrentLineNumber(mExpatParser));
     MaybeStopParser(rv);
   }
diff --git a/parser/xml/src/nsSAXXMLReader.cpp b/parser/xml/src/nsSAXXMLReader.cpp
index 727ab707e453..049cb6c12601 100644
--- a/parser/xml/src/nsSAXXMLReader.cpp
+++ b/parser/xml/src/nsSAXXMLReader.cpp
@@ -81,7 +81,6 @@ NS_IMETHODIMP
 nsSAXXMLReader::HandleStartElement(const char16_t *aName,
                                    const char16_t **aAtts,
                                    uint32_t aAttsCount,
-                                   int32_t aIndex,
                                    uint32_t aLineNumber)
 {
   if (!mContentHandler)
diff --git a/rdf/base/src/nsRDFContentSink.cpp b/rdf/base/src/nsRDFContentSink.cpp
index c45c8e41b459..f58b596b751a 100644
--- a/rdf/base/src/nsRDFContentSink.cpp
+++ b/rdf/base/src/nsRDFContentSink.cpp
@@ -397,7 +397,6 @@ NS_IMETHODIMP
 RDFContentSinkImpl::HandleStartElement(const char16_t *aName, 
                                        const char16_t **aAtts, 
                                        uint32_t aAttsCount, 
-                                       int32_t aIndex, 
                                        uint32_t aLineNumber)
 {
   FlushText();