some problem, I could fix yesterday:
If you like a dark themed KDE Plasma setup (like me), you may be annoyed of GTK+ programs such as Firefox, Thunderbird, LibreOffice, GIMP, … too, which don't respect your Font settings (color and so on) - even if you set it so in System Settings!Here
is the solution: Remove/Rename all .gtk*
-files in your $HOME. You may have to restart the applications.