> For example, an iOS user might prefer Firefox mobile, but their email client may force the link to open in an in-app browser based on Safari.

Hey, wasn’t Firefox on iOS based on Safari related tech anyways?

https://en.m.wikipedia.org/wiki/Firefox

> However, as with all other iOS web browsers, the iOS version uses the WebKit layout engine instead of Gecko due to platform requirements.

I do agree with what you’re saying though! Just those two in particular will probably have pretty good compatibility, which I was amused to find out when I looked into it.