> You tell someone who's dying for a non-webkit browser on iOS

Firefox has struggled to get the sliver of market share they have today. I highly doubt that there are that many people like you and me who crave a real Firefox engine on iOS.

> which is what they should be testing anyway

Having a large part of your team be unable to reproduce bugs is a significant development issue. Some of these operating system features are simply not available outside of the EU.

If it were as easy as you're suggesting, Mozilla would have already done it. Google would have already ported Blink over, or Brave, or whatever browser you prefer. So far I think only Ladybird is really trying to go for a custom browser engine, though app store distribution will be an issue until they can pass enough tests (as Apple has decided your browser is not a real browser if it doesn't pass a certain threshold of existing tests).