I am having problems viewing videos in firefox. it can play sound but the picture just seems to be black. I have uninstalled Flash and then reinstalled. It works for about 10 minutes then the picture goes again. I have done a few virus scans to check if there was any malicious software installed which came back clean. any ideas?
You don't specify it in your question, but if you are using Firefox 4 Beta/RC then you might be the one of many victims of a common Firefox 4 bug, see YouTube.com bug tracking on Mozilla.com