On Android, Firefox lacks per-site process isolation, which makes it less secure than Chromium browsers (not insecure, just less secure.)
With privacy.resistFingerprinting on, Firefox on Android is stuck at 60hz, which I don't like.
There is a noticeable difference in performance between Firefox and Chromium. Firefox is consistently slower when loading webpages, which you notice after using Chromium.
Don't get me wrong, I like Firefox. I use LibreWolf on desktop. I just can't justify using it on Android, at least not yet. Guess I'll go back to using Vanadium.
Gestures are faster and more intuitive. You don't have to do hand gymnastics just to get to the recents apps screen or to go back. The gesture bar can be hidden and it will still work, unlike the buttons which you have to swipe up to bring back, and even when shown it doesn't take up much screen real estate. Apple got it right when they brought gestures to the iPhone and I'm glad Google copied.
First you have to unlock the bootllader. For US (Canada too maybe?) models its straight up impossible. And for models which can be unlocked, Knox gets tripped which leads to a whole host of other problems. Even then, you still don't have custom ROMs to flash. This makes Samsung phones straight up unviable for me. Kind of sad to see when I had a really nice custom ROM experience with my first Samsung in 2014.
I have tried so many keyboards, FOSS one included but nothing is as refined as Gboard without internet access.