Were I not a professional web developer who needs to use the best tools available, and were it not for the awful scroll physics on mobile, I'd probably put up with the rest and use it out of principle.
The odd font rendering is another problem. Fonts in Firefox look different than fonts in other native apps.
Actually what annoys me more on mobile is that chrome seems much better at guessing right where I wanted to touch on non-mobile websites. On HN I can hit the upvote button easily, with Firefox I need to smash several times and sometimes even zoom in in frustration. OTOH I can just install ublock origin on ff mobile and make browsing much faster, especially since I'm using a rather old device; the difference is huge.