I was mainly referring to how every browser app on iOS is forced have Safari underneath. The wiki page on Firefox for iOS [1] mentions this in some detail - it cannot use Gecko like it does on desktop and Android, it must use WebKit instead.

[1] https://en.wikipedia.org/wiki/Firefox_for_iOS

This is a technical detail most people don’t care about. You still get all the competing browsers with all their specific features on iOS, regardless of the rendering engine.

All non-Safari browsers on iOS use the Safari engine underneath, which doesn't currently support WebRTC. It's a pretty huge blocker for a lot of sites (video conferencing, etc) to have to throw up a "Please use Safari" banner for iOS users using anything other than Safari.

It also doesn't support Web APIs that Chrome and Firefox have supported for 8+ years now.

I believe due to webkit no browsers are allowed to do full screen with multitouch. It is possible this only affects Safari and Chrome and isn't a webkit limitation, I haven't tested Firefox.