Is it? It's the only mobile browser I use. I use it on a mid-tier phone (Pixel 5a). It seems fine to me.

Have you tried comparing it with Bromite, Brave or even Chrome? There is a very noticeable difference.

Also, I think Site Isolation* doesn't work in FF Android as it does in FF Desktop. Firefox Android is categorically less secure than its Chromium counterparts.

* https://hacks.mozilla.org/2021/05/introducing-firefox-new-si...

I have not done much comparison, as it works fine for me. I could believe that it is slower, but I still wouldn't call in slow. Perhaps my using an adblocker with FF makes it better for me.

I've only noticed this in very compute intensive SPAs.

But you know what? Having AdBlock makes up for it 10 fold because I never have to see ads on mobile FF.