(I didn't check the download.)

Recently, several users have reported that YouTube generally works more poorly in Firefox since YouTube introduced the "Polymer" design. You could try reverting Firefox to the old design using the following URL or an add-on:

• https://www.youtube.com/?disable_polymer=1
• https://addons.mozilla.org/firefox/addon/youtube-classic/ (I haven't tried this myself)

Any difference?

It seems like the problems is mainly with videos themselves. Went to see if it lags on Chrome, but it seems to just be Firefox.

Hi, running a Beta anything can happen. No information was shared regarding your Video Card Drivers as they do the HTML5 Video so suggest update and or Reinstall. No information on your Extensions/add-ons.

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 ?

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

Yup, doing this made me realize that there was an extension that was active on YouTube page and was causing major perfoance hits. Thanks everyone