Not work anymore. Only sound loudness normalization disabling work.

Flawless. Works perfectly on the current Youtube version. It disable 60fps keeping 2k 4k resolution. Thank you!

It works perfectly on my system!
Thank you so much!!!
h264ify was working fine but the options (e.g. block h264) didn't work until I restarted the browser which was quite annoying.

how to make it work outside of youtube? i need it for other sites too! verypoor!

Firefox 70 x64.... doesnot work. still AVC1

Allows you to disable Audio Normalization. Now you can listen to music on youtube again!

In my limited testing it looks like I can finally watch 4K videos again! My system can handle 4K video, but apparently not 60 fps. Funny thing is in a chromium based browser there is no stutter, and I heard a rumor that if you change the user agent in firefox to chromium it would remove the stutter. You can specify sites to use a different user agent in firefox, you don't have to do it globally.

Is it just me or did google remove the youtube html5 player test as shown in the screenshot?

Nice Add-ons

The seems to have solved the constant freezing I had with youtube vids and with Firefox default vid codecs disabled.