My partner/wife is a long-time iPhone fan. I never tried to convert her, but she is on the point of switching to Android because she can't use Firefox on iOS.
It's completely absurd too - to discard a perfectly fine device otherwise, just because it cannot block ads, or at least, cannot run uBlock Origin (for blocking cookie-banners, social annoyances, etc).
Or is it not "can't use Firefox on iOS" but "doesn't have x feature from Firefox on Desktop"?
Other nice thing of Firefox on Android: being able to listen to Youtube videos even when the screen is turned off.
(I'm sure there are solutions, but many seemed sketchy or didn't work well)
FF can largely do exactly the same thing they do on Desktop to attract people: create a privacy-focused browser (if that's even what they're doing) and things like syncing your bookmarks, passwords, using Firefox VPN, and blocking ads.
Tailscale plus Adguard has finally brought sanity to all my mobile devices thankfully.
Use whatever you want re: iOS or Android, but there are plenty of ad blockers on iOS.