I use PWAs for Firefox and they work ok, although I don’t have the issue you mention. For me, in Ubuntu, if I open a link in a PWA for Google Chat, then the link opens in the PWA firefox window, not my main browser window. Maybe there’s a setting I missed?

Also, the PWA acts like a separate browser, so opening Google Chat requires you to log in again to Google on the same machine. And if you open up a paywalled link, and it opens in the PWA, then you have to log in, even if you’re logged in in Firefox.

Overall 5/7 rating on usability, but did allow me to get completely off of Chrome