Firefox is never going to be a thing as long as humanity moves from desktops to mobiles where changing the built in browser is very uncommon.
That might change soon. Seems the EU is planning to mandate allowing the browser to be changed on iOS.
I have never had mobile FF crash on me, largely been a good experience.
A few months ago they released a version of Nightly that would crash for most users on startup every time. It was up on the Play store for several days.
That would normally be a buyer-beware situation as with any dev build, but Mozilla had purposely locked several important features - such as about:config configuration and loading any extension - behind the Nightly version, forcing users into that kind of experience.