I've been looking for a way to get Gnome's overlay scrollbar working in Firefox. By its appearance, it seems like Firefox is using the standard non-overlay GTK scrollbar, but I haven't found a way to get it to use the overlay version as illustrated below:

I ran across this article with a GTK 2 configuration but despite appearing to attempt to mimic the Gnome appearance, it doesn't seem to work as the scrollbars disappear altogether.
Is there any way to get the overlay scrollbar working in applications like Firefox?