so apparently you can't add a bookmark of a particular page to your home screen on Android if that page happens to be on a site that supports being a progressive web app. it'll just always take you to the site root
The solution I use: turn on Airplane mode, then try to load the site. Firefox will, of course, be unable to load it, but you can still add a shortcut to the homescreen. Doing it this way means you block the PWA manifest that it's loading that takes away all the reasons you loaded it in a web win the first place.
If that doesn't work, you can also put a rule in uBlock to block it, clear all the caches/cookies, and try again. If you need that rule let me know I will grab it.
holy shit it worked