Except you’ve actually changed nothing. Apple forces all third party browsers on their devices to use WebKit (the Safari engine) for the backend, so really all changing browsers does is give you a reskin under Apple’s thumb.

[meme where the hero pulls the mask off the tied-up Firefox’s head, revealing Safari]

I love FireFox and I love my iPhone, but the iOS FireFox app is objectively terrible. I realize that fact is completely Apple’s fault though.

It’s great because I guess your user agent is now Firefox, but actually Apple only allows one Browser engine

If you want to use extensions try out Iceraven (a firefox clone).