I can not figure out why this happens. I tried to play around with all the permissions, reset printer settings on Firefox, created new profiles, all had the same problem. But when I used those same profiles on the apt installation it printed just fine. Is there some weird Flatpak sandboxing happening because I can print fine from the Ungoogled Chromium Flatpak but not Firefox Flatpak.
Just curious but why would you even want to use a flatpack version when there's obviously a better (and working) choice?
I value flatpaks sandboxing and permissions.