The TenFourFox QuickTime Enabler allows you to play selected HTML5 video and audio files and YouTube videos in QuickTime, outside of the browser. You can even play H.264 content with the QTE. This gives you a safer alternative to Flash for many videos.
* Quick Time Enabler – http://adf.ly/hyVkN
If you especially need YouTube support, you may also benefit from installing the MacTubesEnabler.
* MacTubes Enabler – http://adf.ly/hyWIT