I've been using it on my phone for a fair bit. I still run into issues from time to time where pages don't render properly, but that could also have to do with the adblocking which is a major advantage of Firefox. I only use Chrome now if Firefox doesn't work.

I used to use Brave for years, and tried Kiwi for a fair bit too, but both of them have their own issues. I've found that Firefox works well enough for me now and allows me to stick it to the man.