Hi, no information was supplied during making this question on your add-ons/Extensions nor the state of your Video Card Drivers. So this is a shot gun approach. So it is very hard to tell what the issue maybe. HTML5 video is Graphics Card Drivers which Firefox likes to use that are in good shape. So uninstall or reinstall Video Card Drivers or updating with a full version installer VIDEO AUDIO *https://support.google.com/youtube/topic/3014746 - Youtube *https://www.youtube.com/html5/ - Can you support HTML5 *https://support.mozilla.org/en-US/kb/fix-common-audio-and-video-issues *https://support.mozilla.org/en-US/kb/html5-audio-and-video-firefox *https://support.mozilla.org/en-US/kb/fix-video-audio-problems-firefox-windows Extensions can be a issue : SAFE MODE *https://support.mozilla.org/kb/Safe+Mode *https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes In Firefox Safe mode these changes are effective: *all extensions are disabled (about:addons) *default theme is used (no persona) *userChrome.css and userContent.css are ignored (chrome folder) *default toolbar layout is used (file: localstore-safe.rdf) *Javascript JIT compilers are disabled (prefs: javascript.options.*jit) *hardware acceleration is disabled (Options > Advanced > General) *plugins are not affected *preferences are not affected TEST'''''''''is issue still there ?