My biggest frustration with Mozilla, is how they force me to use other browsers for some tasks. I'm a die-hard Firefox user on Mac, Windows, and Android, but if I want to use PWAs then I'm forced to use a Chromium-based browser. This is the most nonsensical decision Mozilla have made about Firefox, but there are other frustrations too - like if I want to configure my keyboard, I have to switch to Chrome to use the VIA configuration app.

It's fine for Mozilla to complain about other platforms/vendors harming them, but they also seem to like shooting themselves in the foot too.