It's clear apple will happily cripple it's own browser to keep people using the app store.
If you yourself want to install PWAs on desktop then chrome, edge, and maybe even desktop safari all do it fine. You won't see the browser's chrome and you probably won't even know it's not running in firefox.
Market share source: https://backlinko.com/browser-market-share
I'd put this more in the category of natural consequences of trying to push a lot of different things forward under one umbrella. Firefox shipped a ton of stuff but there are plenty of cases where the Google team raced ahead on a proposed functionality which reasonable people might have wanted to implement differently, and since PWA was a Google marketing campaign that means that any pressure to implement it is going to be balanced by questions about whether it really benefits many users.
Different browser support a different bunch of these APIs that some people call "PWA".
[0] https://9to5google.com/2021/01/27/firefox-discontinues-work-...