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.
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Seems like a general Firefox issue then. Hope they fix it within the next update. I remember printing working fine so this confirms that an update broke it.
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