If you want to have a browser with a different engine you need a whole different developer account org, you need to maintain two different code bases and you need to very specifically set everything up to pass all of Apple's tests, which are incredibly onerous in time and work, so it doesn't make sense for Mozilla to do so for such a small market share (hell Google doesn't either, and they're a lot bigger than them)
> hell Google doesn't either, and they're a lot bigger than them
It’s more likely that Google is trying to boycott EU initiatives to the extent it can since giving them any support would only turn the public opinion more favorable towards more US tech regulation, and that’s very much against Google’s own interests.