Well, Firefox doesn't support Quicktime video or audio, so it can't be a problem with Firefox. That said, Firefox uses a plugin to stream such content, a plugin that is developed by Apple, I believe. You may need to contact them to get support on this matter.

In any case, it's possible that you are having a problem with some Firefox add-on that is hindering your Firefox's normal behavior. Have you tried disabling all add-ons (just to check, and except Quicktime), to see if Firefox goes back to normal?

Whenever you have a problem with Firefox, whatever it is, you should make sure it's not caused by one (or more than one) of your installed add-ons, be it an extension, a theme or a plugin. To do that easily and cleanly, run Firefox in safe mode (don't forget to select Disable all add-ons when you start safe mode). Of course, safe mode will not help in your case, since it also disables Quicktime. Disable all add-ons (except Quicktime) in normal mode. If the problem disappears, you know it's from an add-on. Enable them one at a time until you find the source of the problem. See this article for information about troubleshooting extensions and themes and this one for plugins.

If you need support for one of your add-ons, you'll have to contact its author.

If the problem does not disappear when all add-ons (except Quicktime) are disabled, you need to contact Apple for support. Unless, of course, you're having problems with all plugins, in which case it's like a problem with Firefox. Please tell me, if that's the case.

You were right. thanks. My lastest add-on, LastPass (which is pretty great), was the problem. I will take it up with them. Thanks again. I have so few add ons I was not familiar with their potential problem.

I'm having this same issue, even when I start in Safe Mode with all add-ons disabled and when I disable the rest of my plugins. Quicktime is up to date. But I can't see video on Apple.com, either (yet I can hear it and see the controls).

I found that if I run Firefox 4 in 64-bit mode and clear the cache, then I can stream videos on apple.com but, only once. If I return to the apple site and try to play a video that I already read before (put in cache), I can't...unless I clear the cache again. Then I can read the videos again, but only once. Very annoying !

I also found that if I run Firefox 4 in 32-bit mode, then streaming videos on apple.com always works!

Hope this will lead us to a real solution !

I am having problems as well. Mine isn't working with .mov or .mp4 but I have tested the mp4 more. Nine times out of ten the video will not play ( no sound or video) If it does play, it will not play again once it has been cached. I have done everything from safe mode to reinstalling plugins. Also from time to time I get a quicktime message that directs me to this page...

http://www.apple.com/quicktime/resources/components.html?os=OSX&ctype=71746578&csubtype=ff9c8000

I installed DivX.. and even included a htaccess with Add Type video/mp4 .mp4 in my files and still nothing.