That is my understanding of how it works. I have Firefox on my phone, but mainly use it to interact with my home server/bookmarks. Everything else is done through Safari for ease of use.
there is a browser on ios that can use chrome and firefox add-ons. it’s called orion. i haven’t checked if it’s open source or not, but ublockorigin works pretty well on it
Not sure what it's like on iOS, but it hasn't been great on Android for me. Had significant lag with pages unfortunately. Don't get the hype at all unless my Firefox install was broken for some reason.
The iOS version certainly works without issue, but it is extremely barebones. Basically no features you’d expect from Firefox. Mostly due to Apple requirements. That being said, I am so thankful I can use Firefox as my desktop browser every day. That’s what really matters to me at this point.