Absolute LIFESAVER!!

I have been using this a few days now, and nearly the only limitation affecting me, fullscreen, is mentioned in the extension info. :) Theater mode doesn't work, and other users say playlists don't work; neither which does not hurt too much in my case, but be wary.

Fortunately (LPT!!) Firefox's picture-in-picture lets you go fullscreen on any PiP-able video, so, all I need to do is click the PiP icon, then double click the player or hit the arrow to go fullscreen.

So no convenient F key shortcut to go fullscreen, BUT:
You can still press C for captions and M to mute as usual, plus pause with space, arrow keys for vol/skip, ,. to frame skip, shift + ,. to change speed, and number keys to jump around.

1. The ability to open YouTube links normally from across the web, plus
2. mostly functional keyboard support
are huge benefits to me versus FreeTube, the open-source app that I tried as a different solution to my recent woes with YT anti-adblock. If this extension isn't for you (e.g. because of the playlist problem) and you don't mind clicking to navigate, check out FreeTube.

Thank you "meeeeemu" for the great extension that's saving my YouTube experience from those god-awful ads.

UPDATE: Doesn't work for age-restricted videos, but they are rare enough that I can find a way to cope