Yes there's extensions.

Had they ever removed extentions?

In beta it does, Stable should get access to the entire addons list around December IIRC

Of course addons that weren't updated with mobility in mind might not work as well.

The Mull version of Firefox has always had extension support, never even knew the official version had even removed it. Mull is otherwise identical with some hardening against tracking and removed telemetry. I've also never had issues with sites breaking which can be otherwise common with hardening

Android extensions work, even on ancient versions. Not all extensions of course, but the important ones.

pretty awesome, especially with extensions. I use it everyday.
In fact, I have two firefoxes. one of them reserved for slack as I don't want to download the app and slack detects that I'm using desktop mode on android(on chromium-based browsers). but Firefox's(with chameleon) spoofing saves my device from one of the worst proprietary applications.