I often use:

Not on mobile, but desktop:

• Enhancer for YouTube, I like it for having the “expand” making the screen bigger also cinema mode, toggling end cards off, boost volume — you can also take screenshots.

• uBlock Origin, of course

• SponsorBlock, which is a big extension that will auto skip sponsor readouts, selfpromos, and a lot of things YouTubers often do (sponsors, self promos, interaction reminders like liking and subscribing, intermissions, intros, previews, jokes, etc - you can choose to skip them or highlight them in the videos) it’s backed by community response, anyone with the extension can set up something to skip and share with everyone. Highly recommend if you’re tired of people pausing the video to talk about raycons or manscaped lol

I may be biased, but I like Lemmy Infinite Scroller. It started out as a 20 minute project just as a proof of concept and then evolved into me trying to make an infinite scroller that works really well. It works well, I can't recall if I made it open-source but I didn't obfuscate the code or anything like that so it's practically open-source anyway even if I didn't make a repo for it. I just published the manifest v3 update of it last week so it's pretty futureproof too.

Other obvious extensions are uBlock Origin, uMatrix, and surprisingly one called Dark Background and Light Text (though DarkReader is also cool too).

Making a note to myself about Sponsorblock and chameleon