most of these are for Chromium browsers because I like Chromium
but if you want firefox versions you can probably find something similar on Add-ons for Firefox.
i'll be linking official websites but when those aren't available I'll just use the Web Store
brings back annotations on all videos that used it before their "removal". i say "removal" in quotes because annotation data wasn't actually removed from YouTube's code, just made invisible to the average viewer.
fixes a lot of old videos that make use of annotations to do point & click adventure games
https://github.com/isaackd/AnnotationsRestored
puts the comments on the side of the screen instead of the bottom. now you can watch videos and read comments at the same time, like on the TV version of YouTube.
https://chromewebstore.google.com/detail/comments-sidebar-for-yout/cgijphidahihhjphcfklefeknhemmdgh
i mainly use this extension for the little options bar under the video, but it has just SO many options for quality of life improvements
https://www.mrfdev.com/enhancer-for-youtube
when reading comments, the new Handles (usernames) will show up instead of the actual display names people choose. this fixes that and reverts it back to how it was before the Handles update
https://github.com/yakisova41/return-youtube-comment-username
there's also a userscript doing the same thing and it has constant updates. so if you want to use it with Tampermonkey or something, here. its on GreasyFork
https://greasyfork.org/en/scripts/468740-restore-youtube-username-from-handle-to-custom
this one's pretty well-known. it returns the YouTube dislike function so you can dislike videos and see dislike counts on other videos. it might not be 100% accurate but atleast it's there. all the youtube rewind videos can now be mocked and disliked forever!
https://www.returnyoutubedislike.com/install
this adds a little speed adjuster in the top right corner of YouTube videos. you can also set and change keybinds to adjust speed. one thing I really like about this extension is that it works with videos across most websites (excluding streaming services i think) so you can use it with a YouTube frontend like Invidious.
https://chromewebstore.google.com/detail/youtube-playback-speed-co/hdannnflhlmdablckfkjpleikpphncik
personally I don't like watching short videos with the Shorts format on my computer because my computer is not my phone. this replaces the /shorts/ part of a youtube link with /watch?v=, the normal YT video player.
for example, youtube.com/shorts/Ciq1ocFLQtE becomes youtube.com/watch?v=Ciq1ocFLQtE
of course if you like watching short videos in the Shorts format on your computer, you don't have to get this one, but I recommend it
https://chromewebstore.google.com/detail/youtube-shorts-block/jiaopdjbehhjgokpphdfgmapkobbnmjp
This adds a little translation button right next to the date indicator in YouTube comments. it seamlessly blends in to the other parts of the comment and functions like how the Translate to English button works on mobile YouTube. highly recommend this one
https://chromewebstore.google.com/detail/youtube-comment-translate/alaejlmlpgcffloicejpccebbeeibemo
"eight extensions? isn't that a little overkill?"
yes
i also have the Stylus extension. here are userstyles i use for youtube
YouTube: The Unbeveling - https://userstyles.world/style/6193/
YouTube for Normal People - https://userstyles.world/style/6258/
Comments Sidebar Dark Mode - https://userstyles.world/style/15177/
i made this one. sorry for shilling my userstyle