Yes I know about PWAs and I am a big supporter. I even experimented with some userchrome.css to emulate a webapp experience, tried the older extension and webapp manager, and the newer "Quick Webapps" by elevenhsoft, and the experience is not really nice.

Used Element web as a Chromium webapp and while not perfect (for example no way to open links with the OS default browser) it is really good.

I just found it odd for Firefox to use GMail as an example, as people using GMail would probably also use Chrome.