I've tried using the firefox shortcut on my phone, and it's less than great (imho). I can't type replies, it goes all janky, freezes up, won't go back to the home page, etc. Virtually unuseable.
I use a zFold 4. Very well could be device. Haven't had any freezing or comment errors. My only issue has been the infinite scroll resetting after a post/comment so you are back at top.
I use kbin as well. As you stated, the interface is appealing.
I just migrated to the Lemmyverse so I'm trying new stuff out but so far, kbin is for me.