Mine same on mac.

Clear the cache and the cookies from sites that cause problems.

• "Clear the Cache": Tools > Options > Advanced > Network > Offline Storage (Cache): "Clear Now"
• "Remove the Cookies" from sites causing problems: Tools > Options > Privacy > Cookies: "Show Cookies"

Start Firefox in Use Troubleshoot Mode in Firefox to check if one of the add-ons is causing the problem (switch to the DEFAULT theme: Tools > Add-ons > Themes).

• Don't make any changes on the Safe mode start window.

See:

• Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems

already cleared the cache, nothing how do i start in safe mode?

I am having the same problem and have tried all of the above and nothing has worked. I know its not my computer as they work in google chrome but I much much prefer firefox to chrome.

I used this link http://forums.adobe.com/thread/1018071?tstart=0

It was real player that was blocking mine to I followed the instructions in this video and I can now watch You Tube with Firefox,

Thank you!! Thank you!! Thank you!! Lorrainespain you have solved my problem! :)

And I can also play games and see videos on Facebook after doing this, so pleased it helped you, I'm hopeless at stuff like this technical stuff !!!!!!!!!!