When ever you hear people trying to convince other people to switch to Firefox the reason is usually moral or ideological. 1
A usually toted reason, is that capitalist browsers like Chrome, Safari & Edge have too much market share. So we need to switch to the less pathologically operated Firefox — t...
You can also get about:config access on Fennec, which is basically just a repackaged Firefox Stable.
It should be said, though, that because of the way Android Firefox is built, this version of about:config is less powerful than that on desktop. Basically, any flags related to the engine will work, but anything that should affect the UI doesn't.
I just checked and about:config is also available on Iceraven (another Firefox derivative)
Also, if anyone (like me) switched away from Fennec because it was flagging as having a vulnerability in it recently, it appears like it's been updated and that issue has been resolved. (I'm switching back because I have found Iceraven feels slower)