(In reply to Fabian Vogt from comment #4) > Display :99 sounds strange. Which display manager do you use? If it's > lightdm, try sddm or gdm. I'm using the default SDDM for KDE Plasma installation. I reproduced this bug on Leap KDE Live CD 1. Install Firefox Flatpak 2. In the Firefox settings, set the opening of pdf files using the system application 3. Download pdf file and open 4. Relogin 5. Try to open it from downloads in Firefox