mouse cursor size in gtk apps

[mattdawolf]

I have 3 50" 4k displays and I sit at least six feet away. Resoltion is set to 2160p. KDE's large cursor theme lets me set it to 64 pixels. When in firefox and thunderbird, the cursor has its own theme and is scaled down to the smallest setting.

Any idea how I can force a setting of 64 pixels for gtk apps? I tried GTK-chtheme but that did not work.