A big advantage of Firefox is (are?) the add-ons / extensions. You can customize it the way you want, and add some good features (video download assist, ad-blocker).
If you use Firefox on desktop, the bookmarks can be sync'd to Firefox mobile.
If you have a fast internet connection, you'll probably notice Firefox to be a little slower than other mobile browsers like chrome. The difference may not be important to you, especially if you don't have a blazing fast connection anyway.
Personally I like chrome browser on my phone, in part because I use chrome on pc (bookmarks and tabs are sync'd). Also it makes login to various google services (I use gmail, drive, sheets, docs, google tasks, gmail calendar etc) easy and convenient. Personally I wouldn't put my google password into a non-google product (browser)... it may be I'm just overly paranoid about that.