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Why doesn't Webm and HTML5 Video doesn't work on youtube with Firefox 4.0b8pre?

Answers: Have 2 answers
I go to http://www.youtube.com/html5 and enable html5. I do not get any video tags or content of the sort.
If I do a search: http://www.youtube.com/results?search_query=gods+gonna+cut+you+down&aq=0&webm=1
None of those videos will appear with the video tag. It will all be adobe flash even though I don't have flash installed. Youtube used to work great with firefox4.0.
The best answer: The problem is with your user agent. it is:
Mozilla/5.0 (X11; Linux x86_64; rv:2.0b8pre) Gecko/20101111 Firefox-4.0/4.0b8pre
While it should be:
Mozilla/5.0 (X11; Linux x86_64; rv:2.0b8pre) Gecko/20101111 Firefox / 4.0b8pre
I have the same problem, and while I do not know its cause, I have found a workaround- install user-agent-switcher.....
Have you installed firefox-4 with the "daily" ppa too?