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And it has extensions like desktop browsers do, including ones that remove even more modern website bloat

You mean built-in extensions or can you add some now?

You have always been able to use every desktop extension on mobile FF, at least as long as I have been using it.

Android or iOS?

Android. iOS's firefox is Safari (like every browser on the iPhone) with a firefox overlay.

This has been possible for as long as I'm using it on Android. Ability to run uBlock is great.