You might want to use Firefox for iPhone and iPad if you use Firefox on the Mac, due to UI similarities for the browser chrome or just for syncing convenience. The Firefox app will sync bookmarks, open tabs across all your devices by logging into your Firefox account. These are the main differences between Firefox and the native Safari app.
I would argue the reasons for using Firefox on iOS are similar, if not exactly the same, to the reasons you’d use Chrome on iOS. The rendering should be identical (I think?). But if you use Chrome or Firefox on the desktop there are a lot of conveniences to using them on iOS.
Due to a service we use at Plain I’ve had to switch to using Chrome on the Mac recently and I sincerely miss the conveniences of using Safari across all platforms. It worked perfectly. Switching to Chrome on iOS would help but it wouldn’t solve the issue since iOS does not allow me to pick Chrome as my default browser.
I’m not the sharpest tool in the barn but why was Microsoft investigated by the Justice Department for the stranglehold that Internet Explorer had on the Windows community and Apple isn’t being forced to allow this same choice on iOS? This is an honest question because I’ve looked into it a little and, while there are some differences (E.g. IE was used to power Windows Explorer on Windows as well. That’d be like Safari powering Finder), I still view this as Apple making a poor choice for the end user.