Same story for me on a OnePlus 5T which is the even older Snapdragon 835. Firefox is genuinely unusable. I tried Mull and Iceraven too. For several months I tried to put up with it, but they were all a slow and buggy mess. Switched to Brave and it works fine.
I use Librewolf on my desktop for the record.
If that's the case it should be a much easier transition. I also came from Ubuntu originally.
You will notice the difference right away. Everything is always up to date so you're not waiting half a year for updates and there's no big upgrade transitions between major versions. And pacman is a lot faster than apt in general.
Plus with the AUR you'll never touch another PPA again. Almost anything you could possibly want is in there, even some of the most obscure/specific things.
I do recommend doing everything from scratch if you have the time, but if not EndeavourOS is literally just preconfigured Arch (and I do mean literally, it uses the same repos) so that's also a solid option.