KDE Plasma 6 global menus for GTK applications (like Firefox)

Hi! I’m trying to configure global menus in KDE Plasma 6. I’ve gotten it working for Qt applications, but have not yet had success making it work for GTK applications. When I run a GTK application (like Firefox), I see this warning in the terminal from which I launched it: Gtk-Message: 20:08:54.284: Failed to load module "appmenu-gtk-module": 'gtk_module_display_init': /run/current-system/sw/lib/gtk-3.0/modules/libwindow-decorations-gtk-module.so: undefined symbol: gtk_module_display_init This...