Bobby responded that the desktop PWA prototype that Mozilla built a few years ago got “some pretty negative feedback” in user testing and they didn’t have the bandwidth to take another crack at it.
I love how much people forget about this. PWAs were not liked when they came out. And that's putting it very very mildly.
And morover, at the time, people in general did not like PWAs as a concept. Independent of the browser. It's a bit funny when nowadays people always ask for PWA support, considering it was once yelled at until it was axed, and the whole concept ridiculed.