--- a/dom/media/MediaTrack.cpp
+++ b/dom/media/MediaTrack.cpp
@@ -31,16 +31,17 @@ NS_IMPL_CYCLE_COLLECTION_INHERITED(Media
 NS_IMPL_ADDREF_INHERITED(MediaTrack, DOMEventTargetHelper)
 NS_IMPL_RELEASE_INHERITED(MediaTrack, DOMEventTargetHelper)
 NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION_INHERITED(MediaTrack)
 NS_INTERFACE_MAP_END_INHERITING(DOMEventTargetHelper)
 
 void
 MediaTrack::SetTrackList(MediaTrackList* aList)
 {
+  SetEnabledInternal(false, FIRE_NO_EVENTS);
   mList = aList;
 }
 
 void
 MediaTrack::Init(nsPIDOMWindowInner* aOwnerWindow)
 {
   BindToOwner(aOwnerWindow);
 }