--- a/dom/html/HTMLMediaElement.cpp
+++ b/dom/html/HTMLMediaElement.cpp
@@ -4268,20 +4268,20 @@ HTMLMediaElement::NotifyMediaStreamTrack
                         this, aTrack->AsAudioStreamTrack() ? "Audio" : "Video",
                         NS_ConvertUTF16toUTF8(id).get()));
 
   if (MediaTrack* t = AudioTracks()->GetTrackById(id)) {
     AudioTracks()->RemoveTrack(t);
   } else if (MediaTrack* t = VideoTracks()->GetTrackById(id)) {
     VideoTracks()->RemoveTrack(t);
   } else {
-    // XXX (bug 1208328) Uncomment this when DOMMediaStream doesn't call
-    // NotifyTrackRemoved multiple times for the same track, i.e., when it
-    // implements the "addtrack" and "removetrack" events.
-    // NS_ASSERTION(false, "MediaStreamTrack ended but did not exist in track lists");
+    NS_ASSERTION(aTrack->AsVideoStreamTrack() && !IsVideo(),
+                 "MediaStreamTrack ended but did not exist in track lists. "
+                 "This is only allowed if a video element ends and we are an "
+                 "audio element.");
     return;
   }
 }
 
 
 void HTMLMediaElement::ProcessMediaFragmentURI()
 {
   nsMediaFragmentURIParser parser(mLoadingSrc);