You can use any browser of your choice if its a Microsoft Edge theme.
You can always switch operating systems if you don't like this after all.
Not trying to defend either, it's just the double standards feel puzzling to me.
Right now, Apple's smartphone market share in the USA is only 50%. Microsoft's Windows is probably at 80%+ of the desktop market.
They are talking about iOS.
It's not literally a "skin", Firefox on iOS is actually a separate Apple-approved app. It's just that they're forced to embed the Safari engine rather than using Gecko for it.
As for iOS: yes stuck with safari as default.
A worse offence is having a platform so locked down that clearing opened apps from the recents menu has to be done one by one instead of having a simple single "clear all" solution the alternative to which is using a 'tweak' which would necessitate having a jailbroken phone which would, in turn, involve connecting the phone to a computer to get jailbroken on each restart or a more convoluted method.
Another widely-known issue: when using apps with an alternative store like AltStore without jailbreak, you either need to connect to a Windows/MacOS or use some tweak to have on-device signing enabled within every seven days unless you have a Apple Developer subscription.
Moreover, iOS has "slide to poweroff" but there is no convenient way to restart[1]: Xiaomi copied the UX and even made it better by needing less steps. Even simple changes requiring steps so radical (perhaps not as radical as flashing a 'custom ROM' but is IMO less rewarding than the latter) and regular maintenance is telling.