WebM video seems to be broken

Question

I just installed FF 4 on Mac OS 10.6.7 (current as of 2 days ago), and I can't get any Webm videos to play. This goes for the [http://www.mozilla.com/en-US/firefox/4.0/firstrun/ main landing page], YouTube html 5 trial, and a number of other sites I tried.
On the Firefox first-run page, the content pane pops up with the poster image, but appears grayed-out with an "X" over it. On YouTube, the player shows a spinning icon (the same one as when a clip is normally loading) indefinitely and never actually plays. [http://camendesign.com/code/video_for_everybody/test.html Here], too, I get nothing but a gray box with an "X."
Interestingly, [http://devfiles.myopera.com/articles/1891/sunflower-webm.html this bee] does play, but is extremely choppy, and [http://devfiles.myopera.com/articles/1891/custom-controls-webm-720p.html this trailer] actually plays beautifully.
A couple of important things:
1. This is Firefox-specific--oddly, I thought at first that it was affecting Chrome, too, but that's not the case now. Go figure.
2. I DID try this on a clean profile with an empty cache. After a reboot. No dice.
3. FWIW, I tried with the Mac OS firewall off--again, no difference.
Any help that anyone can offer will be much appreciated!
Danny

Answer 1

ok, two things you can try:
1) rerun the config wizard, let it install the Help collection/feature again. Rerun will not hurt but it will cause outage during the running period. if this is prod so plan accordingly.
2) if above did not work( i am sure it will). 
follow these steps to directly install the help collections:
Click Start,
click Run, type cmd,
and then click OK.
At the command prompt, type the following command, and then
press ENTER:
cd %COMMONPROGRAMFILES%\Microsoft Shared\web server extensions\15\BIN
At the command prompt, type the following command, and then
press ENTER:
Hcinstal.exe /act InstallAllHCs /loc
1033
After you run the command, you are presented with a return code that informs you of the result of the operation:
•Return code 4 means that the operation was successful.
•Return code 32 means that no action was taken.
•Return code 256 means that the operation failed.
Please remember to mark your question as answered &Vote helpful,if this solves/helps your problem. ****************************************************************************************** Thanks -WS MCITP(SharePoint 2010, 2013) Blog: http://wscheema.com/blog