When I upgraded to Firefox 4 on my iMac, OSX 10.6, it no longer played QuickTime video or audio properly. The symptoms tend to be inconsistent. Sometimes the audio would play but not the video. Sometimes the video would play but blink off and on with a white screen. Mp3 files will not play at all on some occasions and will play partially on others. When I removed Firefox 4 and reinstalled 3.5, everything worked fine again. Anyone have a suggestion?