I decided to switch from Safari to Firefox mainly because it looks better and has dark mode but I switched back to Safari. Firefox has basically no 3D Touch features and some websites won’t work properly until you disable tracking protection.
I use Safari mostly. Firefox is usually reserved for doing things that aren't for me and/or if I simply want a browsing data purge on quit. I also use it if/when Safari doesn't do the right thing… if it doesn't work in Firefox it isn't going to work. Chrome I use the least but it has some specific tasks… like my service provider's PVR system requires Chrome.