Or eg. for BandCamp I wrote a script that hides the play progress bar so that I can actually focus on the music instead of how many seconds of music there are left.
I'm referring to Android versions. No extensions allowed on Android Chrome, but Kiwi does. Android Firefox allows some small number of extensions, but IceRaven allows many more.
Have you tried out LibreWolf? By default its a bit hard to use since it doesnt save passwords or history or cookies or anything, but you can turn all that on. Its a fork of firefox meant to be more privacy focused. You can still use your firefox account and everything im pretty sure.