diff --git a/js/setup.js b/js/setup.js
index 7133186..3a4e069 100755
--- a/js/setup.js
+++ b/js/setup.js
@@ -208,16 +208,23 @@ addEventListener( "DOMContentLoaded", function() {
   
   // Initialization to take place after media (and Butter)? is ready.
   function initAfterMediaReady () {
+    // HTTP/1.0 servers can cause audio elements to break silently. We want them to break loudly.
     var duration = popcorn.duration(),
         originalTime = popcorn.currentTime(),
         targetTime = 0;
 
+    // .duration breaks in Firefox:
+    if ( isNaN( duration ) ) {
+      throw new Error( "popcorn.duration() is NaN.")
+    }
+
     if ( originalTime === targetTime ) {
       targetTime += popcorn.duration() / 2;
     }
 
     popcorn.currentTime( targetTime );
 
+    // .currentTime breaks in Chrome:
     if ( popcorn.currentTime() === originalTime ) {
       throw new Error( "Calling popcorn.currentTime(x) did not affect the value of popcorn.currentTime()." );
     }