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Firefox will support at least 200 new extensions on Android this December
(www.androidpolice.com)
This is a most excellent place for technology news and articles.
YT on Firefox Mobile has the added benefit of letting you swap to desktop mode and play videos with the screen off, no YT Premium needed ;)
Been doing this for years, but if too much of a hack for you, NewPipe also supports background video, and downloading video, or just the audio, which is great if you have a lot of long form audio-focused channels like music reviews, videoessay content, etc.