In years past Firefox would occasionally crash on me, but I'm not sure it's ever even done that on my current phone, which is closing in on 9 months old. I'm not exactly treating it kindly either, I currently have 93 "tabs" open and though it doesn't keep those in memory it does recall page position even if it has to reload the original source when I go back (based on it putting me at the same point on the page for a week-old HN thread I was skimming through).
There are some addons I'd recommend bypassing on mobile though just for UI reasons - uMatrix, any of the Vim keybinding options, stuff like that. Also, unfortunately the Invert Colors addon doesn't work on Android because of a missing API.