diff --git a/.editorconfig b/.editorconfig
new file mode 100644
index 0000000..11d38ee
--- /dev/null
+++ b/.editorconfig
@@ -0,0 +1,7 @@
+root = true
+
+[*]
+charset = utf-8
+insert_final_newline = true
+indent_size = 2
+indent_style = space
diff --git a/extensions/adventofcodetimer/advent_of_code_timer-0.1-fx.xpi b/extensions/adventofcodetimer/advent_of_code_timer-0.1-fx.xpi
new file mode 100644
index 0000000..64e7753
Binary files /dev/null and b/extensions/adventofcodetimer/advent_of_code_timer-0.1-fx.xpi differ
diff --git a/extensions/adventofcodetimer/index.html b/extensions/adventofcodetimer/index.html
new file mode 100644
index 0000000..bfba1e1
--- /dev/null
+++ b/extensions/adventofcodetimer/index.html
@@ -0,0 +1,22 @@
+<!DOCTYPE html>
+<html lang="en">
+<head>
+  <meta charset="UTF-8">
+  <meta http-equiv="X-UA-Compatible" content="IE=edge">
+  <meta name="viewport" content="width=device-width, initial-scale=1.0">
+  <title>Advent of code timer</title>
+</head>
+<body>
+  <h2>Advent of Code Timer</h2>
+  <p>
+    A simple Firefox browser extension that times how long it takes you to do the daily challenges on <a href="https://adventofcode.com/">Advent of Code</a>.
+  </p>
+  <p>
+    The timing is started manually when a day is viewed and ends when both daily challenges have been completed.
+    Times are displayed to the right of each day in the calendar view.
+  </p>
+  <p>
+    Click <a href="advent_of_code_timer-0.1-fx.xpi">here</a> to install the extension. Have a good day :D
+  </p>
+</body>
+</html>
diff --git a/extensions/adventofcodetimer/updates.json b/extensions/adventofcodetimer/updates.json
new file mode 100644
index 0000000..69c01b1
--- /dev/null
+++ b/extensions/adventofcodetimer/updates.json
@@ -0,0 +1,12 @@
+{
+  "addons": {
+    "adventofcodetimer@widauer.dev": {
+      "updates": [
+        {
+          "version": "0.1",
+          "update_link": "https://widauer.dev/extensions/adventofcodetimer/advent_of_code_timer-0.1-fx.xpi"
+        }
+      ]
+    }
+  }
+}
\ No newline at end of file
diff --git a/index.html b/index.html
index 35245c3..4aec72f 100644
--- a/index.html
+++ b/index.html
@@ -11,6 +11,7 @@
     <ul>
         <li><a href="pi">pi</a></li>
         <li><a href="vcfsplit">vcfsplit</a></li>
+		<li><a href="extensions/adventofcodetimer/index.html">Advent of Code Timer</a></li>
     </ul>
 </body>
 </html>
\ No newline at end of file
