:like:

For some reason it stopped working on my current esr build 52 of firefox So I searched for older versions of EFY (ALL versions including the latest were working yesterday!!!!). I have compatibility checks disabled in about:config. I installed one from 2018 and it works just fine except for the autoplay pause that only kicks in after 20 or 30 seconds for each video I open in a background tab instead of instantly. This is Youtube's aka Google the Anitchrist's fault.

Firefox 71 has broken this extension, have tried removing & re-installing still broken. Was superb before FF71.

I'm very happy with this addon it gives me what I need on youtube (slow/fast speed, default *4K, HD).
I wish this kind of add-on can be added on android ;) (mmh maybe it can)

*Sometimes, it doesn't shows the 4K as default (why?).

This addon is very helpfull but it has some bugs - it spams many same elements (style and script - including usermade) into head of document. It can make browser slower as well as it takes more memory.

I love all the little adjustments the extension allows, as well as the customisation, which is a very nice aspect that YouTube itself doesn't seem to care much for. However, there seems to be a conflict with the Remove Youtube Suggestions extension which causes it to not work, so I'm forced to keep it turned off :/
I hope the conflict is fixed soon, so I can go back to using this.