Sometimes the QuickTime plugins are not detected properly.

see if QuickTime is installed and working, in Testing QuickTime in this link : Using the QuickTime plugin with Firefox .

see also: QuickTime .

thank you

Please mark "Solved" the answer that really solve the problem, to help others with a similar problem.

I finally figured out how to solve this problem. Once I made the move to Mountain Lion via clean install, Quicktime stopped working in FF, but it worked in all my other Mac browsers. The Quicktime plugin will only first register as an FF plugin when you run FF in 32-bit mode. So I quit FF, went to the Applications folder, did a "Get Info" on FF, checked the 32-bit mode box, re-ran FF, was able to see an online Quicktime video (trailers.apple.com), then quit FF, unchecked the 32-bit mode setting, and all is right in the world again.

I actually gave up on FF after all these years and tried to switch full-time to Google Chrome. That did not go as well as I expected, and so I had to figure out the FF problem or else I was going to go mad!

I was thrilled when I read this and went off to implement it. When I opened the 'get info' box I did not find anywhere to select 32-bit mode. Can you help me? I am on Lion.

Allenjbj, you should see the attached window when you do a "Get Info" on the Firefox app.

My "get info" does not look like that. I am on Version 12 and it says I'm up to date. Under the general tab I have the "locked" check box but not the one above it to select 32 but mode. Is this because I'm on Mac?

I am on a Mac as well. I believe this option is only available on Macs. Which version of the Mac OS are you running?

I am running Lion, 10.7.4

Can you post a screenshot of your full "Get Info" window for the Firefox app?

Yes, here it is.

What model Mac do you have?

MakBookPro 4,1 I believe that is called a late 2008 when I looked to see if I could upgrade to Mountain Lion, which I plan to do soon.

I'm wondering if your Mac supports 64-bit. I think it does if it is a late 2008 model, but I'm not sure. If not, then that means it is running in 32-bit, which also means that the Quicktime issue should resolve itself. Strange...

It does support 64 bit. I appreciate your assistance. I guess I'll just have to switch to Chrome.

I seem to remember some option when installing Lion regarding 32 vs 64 bit mode. I think I may have selected 64 bit since I didn't have any programs that appeared to need 32bit. I cannot find anything on this in a few quick searches but I'll keep looking.

You do have the option to either boot into 32 or 64 bit mode on the Mac (http://9to5mac.com/2011/03/20/new-macbook-pros-default-boot-in-64-bit-mode/). Maybe that will help.

I would also recommend downloading and installing the latest version of Firefox, v.15, just to see if that makes a difference for you.

I updated Firefox - nothing changed. I will try booting in 32bit mode from your example and see if it helps. Thanks.

I rebooted using the 3 and 2 keys to force the boot in 32bit mode. I restarted Firefox but it was not corrected. I checked the 'get info' screen and the option to start Firefox in 32bit mode was present this time. I selected it and restarted Firefox. IT CORRECTED MY PROBLEM.

Thanks a bunch!

Sweet! Glad to hear! Now never speak of switching to Chrome ever again :-) LOL

THANK YOU! I have had this problem and got me pissed but your simple solution worked like a charm. I tried Chrome but it had to many limitations compared to FF so here i am.