Hi, Please try to '''Delete all''' the existing Flash cache in the Windows Control Panel > '''Flash Player''' > '''Advanced''' as well as '''Clear Now''' the '''Cache''', '''Cookies''', and '''Site Preferences''' in Firefox '''Tools''' ('''Alt''' + '''T''') > [https://support.mozilla.org/en-US/kb/Clear%20Recent%20History Clear Recent History]. You may also have to fully re-trust Firefox + its processes/files in all the configuration areas/modules of any and all security software (antivirus, firewall). Please see [https://support.mozilla.org/en-US/kb/Firewalls this]. [http://kb.mozillazine.org/Firewalls AV/Firewalls Configuration] If the problem persists, you can also try the [https://addons.mozilla.org/en-US/firefox/addon/ie-tab-plus/ IE Tab] + or the [https://addons.mozilla.org/en-US/firefox/addon/ie-tab/ IE Tab] add-on to temporarily watch problematic Flash content inside Firefox.

Tried above steps, did not work.

Try to opt-out of HTML5 video on YouTube. *http://www.youtube.com/html5/ *[https://bugzilla.mozilla.org/show_bug.cgi?id=775491 bug 775491] - HTML5 unresponsive script errors on YouTube <i>([https://bugzilla.mozilla.org/page.cgi?id=etiquette.html please do not comment in bug reports])</i>

Thank you. it was the html five.

You're welcome

Thank you - I thought it was the old problem with Flash Player 11 in a new disguise, but opting out of the HTML5 trial sorted it for me.