Chrome opacity in Firefox/Linux

So maybe some of you have seen that in GNOME 2.30, the per-widget transparency enabled by GTK+ 2.18's client-side windows has been taken advantage of, e.g. in gnome-terminal. This enables the "semi-translucent chrome" effect often seen in Windows Vista/7 with applications such as Windows Explorer, IE, and Firefox.

Does anyone know if there is an extension, setting, or future plan to do this sort of thing in the Linux version of Firefox? Google reveals nothing directly relevant or useful.