I have laptop Lenovo Y-50-70 with 240 DPI screen and Tumbleweed with Plasma 5 on it.
My display scale factor is set to 2, and before last update (24.01.2018, it brings ± 200 updates) all worked fine.
But after update my Firefox and Thunderbird have been ignoring scale factor and other Plasma settings such force font’s DPI, and have too small interface and fonts.
There was no updates of Firefox and Thunderbird itself.
I have only standard tumbleweed repositories + packman.
These variables are not set in my system because this section on startkde is not executed:
if "$kdeglobals_kscreen_screenscalefactors" ]; then
export QT_SCREEN_SCALE_FACTORS="$kdeglobals_kscreen_screenscalefactors"
export GDK_SCALE=$kdeglobals_kscreen_scalefactor
export GDK_DPI_SCALE=`awk "BEGIN {print 1/$kdeglobals_kscreen_scalefactor}"`
fi
You should not change anything in startkde. And that of course won’t have any effect if it is not executed.
But again, it should be executed (and the variables set) if you changed the scaling settings.
What does your ~/.config/startupconfig file contain?
Well, I can’t try with Firefox (because I’m on 42.3 with a GTK2 based Firefox), but those GDK_* variables do work with other GTK3 applications like gedit here.
You do use the standard Firefox 57 from the standard repos?
In startkde i changed it to force set variables. But even without it running firefox as GDK_*=… firefox has no effect. Firefox is from standard repos, 57.0.7.
I originally set the Firefox “layout.css.devPixelsPerPx” in Leap-42.1 and it has survived migrations through 42.2 to Tumbleweed (Plasma5 and Openbox-KDE) without any trouble.
PPS, as I just tried it myself on a Krypton LiveCD (based on Tumbleweed with the latest unstable KDE packages):
Those GDK_* variables do affect Firefox.
But setting both the way I suggested will actually force a scaling of 1 (as explained in the bug report).
Either of this would scale Firefox by a factor of 2: