Unless they changed it, mobile Firefox is locked to a limited set of extensions unless you:

1. Use Nightly.
2. Create a Mozilla account.
3. Log in to that account on the Add-Ons site and create an add-on collection with all the extensions you want to install.
4. Set that collection as your source of add-ons in the Firefox settings.

You're also unable to use about:config unless you're using Nightly (or maybe Beta). So Nightly is really the only version worth using since it doesn't have nearly as many artificial restrictions as the stable version does. This is also true to a lesser extent on desktop where you have to use Nightly to install unsigned extensions.

You also can't open any offline HTML files for whatever reason and on devices with very little RAM (like 2GB) Firefox isn't viable, but Chrome-based browsers work mostly fine. Firefox is still the best mobile browser though, mostly because it supports extensions at all.

Photon seems to have a semantic layout that firefox detects as settable into reader mode.

My personal gripe with mobile Firefox is searching by using the address bar.

I have had countless times where I put in my search prompt, followed by pressing the little X all the way on the right and thus clearing the address bar. My brain just really expects an enter button to be there.

I think my current record is entering a search term and then clearing it literally directly 3 times in a row, getting more and more confused each time.

Any other “gotchas” that you guys have encountered on mobile FF?

Not specific to Lemmy, but I was ... impressed ... that it is impossible to set a custom homepage in the browser. Something that is possible since 15+ years in every mobile browser I used.