Things got a bit better over time, but unfortunately the thing that eventually fixed it was when I got a new phone. Now I get around 2-3 90Hz frames, which is still worse than chrome, but far less noticeable. I have not measured "New Firefox"/Fenix/Preview yet, but it does feel like it's a bit closer to chrome.
Whenever I've tried other browsers - Chrome, Brave, DDG - having to click "I accept" on every single webpage to remove the "This site uses cookies!" pop-up is really tedious. I hope the Firefox on Mobile add-ons support doesn't just start and end at ublock origin.
(I don't use uBlock on mobile, but I might go look into it...)
My only complaint is that it doesn't integrate quite as well as Chrome, but I don't think that's Mozilla's fault.
There's a reason Mozilla is rewriting the whole thing.
That LG v35 outspecs my BlackBerry KEYone by a good margin, and Firefox is just as fast as Chrome for me. Which is to say, snappy.
I read more details about your performance problems in another comment, and it sounds horrible; I can't imagine anyone using that. Sounds like a nasty bug, I guess..?
That said, new Firefox mobile is way faster and the nightly build already has uBlock support. Best of both worlds.