Flatpak Firefox displays certain pdfs incorrectly


Was using Mozilla Firefox installed via flatpak. Certain pdfs display correctly but other pdfs displayed with Firefox (either locally or online) are displayed badly: spaces are replaced with a lower half block character, fonts not sharp. I installed Firefox from the openSUSE repos (not from flathub) and opened the same pdf and it displayed correctly. I downloaded the pdf and opened it using Okular and no problems. I also opened the “troublesome” pdfs on Firefox in Windows and it displays correctly. I conclude that the flatpak version of Firefox is causing some pdfs to display incorrectly but I don’t know why.

I installed flatseal to tweak the flatpak Firefox’s settings but nothing seemed to fix the pdf display issue. Please see screenshot below of how Firefox (from openSUSE, on the left hand side) and Firefox (from flathub, on the right hand side) display the same pdf from the internet. The online pdf in the screenshot and used as an example of the issue can be found at:


Not sure why some pdfs display correctly in Firefox from flathub and others display incorrectly. I’d prefer to use flatpak’s sandboxed Firefox if possible. Is there anyone else with the same problem or someone who who found a solution to this issue?



Perhaps this may be relevant…

Thanks. I was wondering that also but many other pdfs do display correctly and there are many that don’t. Also the other flatpak apps that I have installed seem to have problems with font issues. I thought pdf readers are able to display fonts correctly even if certain fonts are not installed in the system. Is that correct?