No Breeze theme in Firefox in Flatpak

I am using KDE in F39. Installed Firefox as flatpak. But firefox only use gtk theme. How do I apply Breeze theme in flatpak version of firefox?

This seems to fix the issue:

flatpak override --user --filesystem=xdg-config/gtk-3.0 org.mozilla.firefox

This is meant to work automatically. For posterity, are you using Wayland or X?

Also, is org.gtk.Gtk3theme.Breeze installed? If so, do you recall if you did that manually?