Hi guys - for me this helped. If Flash player is working in IE, then: Close Firefox - open Internet Explorer - got to the Adobe Flash Player Site:

http://get.adobe.com/de/flashplayer/

In IE you can see there is the 64-bit version - (in Firefox there was just the 32-bit version) - get to: (others)

http://get.adobe.com/de/flashplayer/otherversions/

choose your system and version download it via internet explorer and install the adobe flash player restart firefox and it should work. helped me after wasting one day of my life to find a solution, alle sites work just fine now. hope this helps.

The site you provided (http://get.adobe.com/flashplayer/otherversions/) gives access to the 32 bit version only. I had the 64 bit version from http://www.filehippo.com/download_flashplayer_firefox_64/

My system is protected by Rollback Rx so, frustrated by the problem, I decided to rollback to prior to the v13.0 update. All was well again and yet I decided to try one more thing, update the Flash player plugin from v11.2.202.235 to v11.3.300.257 and again it stopped working.

In summary, at least where my system is concerned, the culprit is not Firefox v13.0, it's the latest Flash player plugin.

Update: Seems I'm not the only one. See this post on Adobe's own forum: http://forums.adobe.com/message/4484664

A http://is.gd/GLOdgZ Google search shows there are plenty of people complaining on various forums.