We tried to bring scaling to GTK apps in Bug 387849. But it caused issues (e.g. Bug 389523) and had to be reverted. We should sort out whatever tweaks need to be made here and give it another go. Lack of automatic scaling support for GTK apps hurts our platform given the quantity of popular GTK apps (Firefox, Thunderbird, LibreOffice, Inkscape...) One final note: Using the Font DPI for scaling purposes is a nasty hack. We should consider whether or not this works from the perspective of using KScreen scaling alone, not in conjunction with the "Force Fonts DPI" setting in the Fonts KCM.
Actually this was silly. There's no reason to open a new bug when I can just re-open Bug 387849. *** This bug has been marked as a duplicate of bug 387849 ***