Some combinations of add-ons and settings appear to be incompatible with Flash 11.3. Check this article and see whether it helps: Flash 11.3 doesn't load video in Firefox.

See:

• https://support.mozilla.org/kb/flash-113-doesnt-load-video-firefox
• https://support.mozilla.org/kb/keep-flash-up-to-date-and-troubleshoot-problems

• http://forums.adobe.com/thread/1018071?tstart=0
• http://blogs.adobe.com/asset/2012/06/inside-flash-player-protected-mode-for-firefox.html

Simple fix. Go to uninstall programs and uninstall the flash player plugin. Not he player, just the plugin. Should work fine after that.

Hi cpldube, if you uninstall the Flash player plugin, then the next time you visit a page that uses Flash, Firefox will prompt you to install it again. I'm not sure how that helps...