That said, I think there is a fundamental difference between Apple's behaviour and Mozilla's here, for the simple reason that users of Apple gear paid for it and should therefore get what they bought, in proper working order. While it's certainly frustrating for many Firefox users that things keep changing and often not for the better recently, those users never paid Mozilla anything and so Mozilla owes them nothing in return.
Things get much more complicated when you bought the device from a vendor but the ultimate control rests with some third party, typically a software developer. This is where a lot of dubious things are going on right now, but in a lot of jurisdictions the consumer protection laws haven't yet adapted to the modern technology landscape and tend to place the original vendor with most or all of the responsibility when things go wrong, even though it's actually the software they're reselling that is the root cause of the customer's complaint. At some point we're going to have to deal with this, along with the various other third party issues like the legal basis (or otherwise) for an EULA or similar document, because clearly it's not realistic for every shop or web site that lets you buy a device or a copy of some software to fix technical issues they have no practical way to control.