[System] Font rendering issues in Firefox (and GTK apps)

[apogiee]

Firefox - and all GTK apps in general - seem to ignore the KDE sub-pixel rendering settings, and fontconfig on Wayland. GTK apps use grayscale font rendering instead, resulting in a noticeably worse experience making all fonts seems fuzzier and blurrier at the same time compared to how crisp they appear in Cinnamon (presumably Gnome too). Screenshots for comparison: https://imgur.com/a/H8h1Oeb

After hours of trying to fix this I found that gsettings is forcing grayscale by default:

gsettings list-recursively | grep alias

Changing that to rgba does help a bit:

gsettings set org.gnome.desktop.interface font-antialiasing rgba

But this only affects some GTK apps, and in case of Firefox it only changes grayscale rendering to rgb for some websites. Many others, like Reddit for example or even this forum, are still stuck at using grayscale even with this settings. Sites, that do render properly with rgb sub-pixel rendering under Cinnamon.


Is there any way to fix this properly, and to ensure proper rgb sub-pixel rendering is used under Wayland?

[Princey]

Question, are you using the default install (snaps) of Firefox?

[apogiee]

Question, are you using the default install (snaps) of Firefox?

Yes, this is with the default snap install. But I also managed to install and run a flatpak version, and it behaves exactly the same. And as a matter of fact you can easily reproduce this issue just by running the live session, loading any web page with Firefox and taking a screenshot of some text. Zooming in you should see grayscale is being used.

[Princey]

I do not use snaps at all. First thing I do on a clean install is remove snaps. I ran the native version (deb from mozilla) of Firefox so I don't have that issue.