Hey. Have really no idea what kind of problem that is. There are some video services which just stopped workin in my Firefox 22. It could be a issue with some sort of addon (is there a way to give you a plugin list?).
I just get a black window on videos i get from for example twitch.tv, moviepilot.de. Youtube works without problems. They work on other browers like opera. Flash, Quicktime, Java are installed with their current version. Is there any other video-player-stream-thing I missed out?