What site is the html5 coming from? Also could be a hardware limit as well.

Hi it should play HTML5: VIDEO/AUDIO *https://support.google.com/youtube/topic/3014746 *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 If still have issues as no info came regarding what extensions you are running or your video card drivers (if have errors would have been able to help) please try : 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 ? Please let us know if this solved your issue or if need further assistance.

It was coming from MSN.com. the advertisements were in HTML5 and froze so content wouldn't load because advertisement didn't play.

You responding to Westend or the info I supplied ? What extensions are you running please, list them. What happens in Safe Mode. ??