So, not uBlock or whatever as everyone’s aware of that.
Mine (all Firefox):
Video Speed Controller. LOVE this one. A tiny widget appears on any video showing current speed and you hit a key to +10% / -10% (I have mine mapped to [ and ]). You can also hide the little widget (v) if you’re watching a movie etc.
Very handy for sites that don’t support changing video speed or have limited options.
Quick cookie manager - Allows you to delete all cookies on a page that you’ve visited. Very handy when “reject all” leaves you with like 20 cookies anyway.
Netflux - 1080p Netflix on Linux. Can be a little fiddly at times but it does work.
WebToEpub - convert Web Novels (and other web pages) into an EPUB for offline reading. Works with many sites, including: 1. ArchiveOfOurOwn.org 2. FanFiction.net. 3. royalroadl.com
etc…
Works well, although I would recommend supporting the official release or giving the authors some sort of $$. Its helped archive a couple of old comics, stories, and fan fictions of terrible quality ;).