I have a strange problem with videos in Firefox:
After a while videos played via a HTML5 video player only show a black screen, when actually being played.
The videos play just fine when I restart Firefox or when I play them in Chrome. Also, the audio of the video plays without problems and I can see the preview image before playing. This happens with YouTube, Vimeo and other players.
Please see here for a demonstration: http://www.screencast.com/t/kkFlEk0nup
Any idea what could be the reason and how to fix it?