I’m not sure how firefox does it but I don’t think pwas themselves have control over this. Sounds like a feature request for firefox to me.

For what it's worth, Vanadium (based on Chromium, so I'm assuming Chromium, Google Chrome, and most other Chromium variants will as well) shows the PWAs in the history, too.

Must be a Firefox issue. I installed through safari and voyager history doesn’t show up in my browser.