Make Firefox ProfileManager use GTK Dark Theme

While you can set a preference in your profile configuration to allow Firefox (Waterfox in my case) to use the dark variant of your GTK theme, this preference logically does not affect the Profile Manager.

While you can use env MOZ_ALLOW_GTK_DARK_THEME=1 waterfox -P, it’s a little bit inconvenient because for your desktop application you would have to change your .desktop file that will be overwritten by the next update.

But, if I’m right, you can use /path/to/firefox_directory/defaults/prefs/allow-gtk-dark.js and set the preference there via pref("widget.chrome.allow-gtk-dark-theme", true).

There you go!