No longer works. YouTube probably changed something yet again, and broke it. This is the problem with unmaintained add-ons, they quickly become obsolete. Sadly there are no functioning alternatives, so I'm forced by YouTube to use the AV1 codec, even though my hardware is too slow to use it without stuttering. Even setting media.av1.enabled to false has no effect any more. Mozilla seems to think that every PC user can afford 2020 hardware. At this rate, I'm just going to have to stop using YouTube, unless Google/Alphabet/Whatever wants to send me a new PC.

Does't work

seriously this should be available from youtube natively.
what does Google think, that everyone jups on 3xxx series gpu's soon as they are available, as they are the only ones with hardware support for av1 codec currently.
so why not offer option for vp9 if my machine can easily do 8k 60fps on vp9, but struggles on 4k av1.

Works great.

This causes YouTube to load low-res version of videos though :/

Pablito Alfredo salvador favre
0910326081
Cédula de ciudadanía de sudamericanos
Guayaquil ecuador sudamericano

работает, но.. весь контент уж давно в новом кодеке вп89, а мп4 уже и не видно, максимум увидите авц
¯\_(ツ)_/¯

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!