Try to delete the pluginreg.dat file in the Firefox Profile Folder and maybe addons.sqlite as well to reset the plugin registry databases. See Re-initializing the plugins database: *https://support.mozilla.org/kb/troubleshoot-issues-with-plugins-fix-problems You can use this button to go to the current Firefox profile folder: *Help > Troubleshooting Information > Profile Directory: Show Folder (Linux: Open Directory; Mac: Show in Finder) *http://kb.mozillazine.org/Profile_folder_-_Firefox ---- You can check for problems with current Shockwave Flash plugin versions and try this: *make sure you have the latest Flash version:<br>http://www.adobe.com/special/products/flashplayer/fp_distribution3.html *check for updates for your graphics drive drivers<br>https://support.mozilla.org/kb/upgrade-graphics-drivers-use-hardware-acceleration *disable protected mode in the Flash plugin (Windows Vista and later)<br>https://support.mozilla.org/kb/adobe-flash-protected-mode-firefox *disable hardware acceleration in the Flash plugin<br>https://helpx.adobe.com/flash-player/kb/video-playback-issues.html *disable hardware acceleration in Firefox<br />https://support.mozilla.org/kb/upgrade-graphics-drivers-use-hardware-acceleration See also: *http://kb.mozillazine.org/Flash#Troubleshooting