Hackinations: That Firefox full-screen thing

Got dual monitors? Have Firefox installed? Go ahead an open a browser window and then do this. Either click F11 or choose View > Full Screen (Command-Shift-F). Firefox then does something that Lion users have been clamoring for.

It creates a Lion-style full-screen presentation, complete with the double-arrowed OS X-standard restore button. And it does this only on one screen. (Update: It has hover-to-reveal of the restore button, which doesn't seem to be a custom behavior.)

I'm dying to know how. All the other apps that support full-screen use the standard zoom item built into their windows. I showed you how to add that feature to non-full-screen apps in a recent Hackinations post. But the standard zoom goes across all windows, not just on one.

How is Firefox doing it? I don't know and I'd like to find out how. And, more importantly, I'd like to find out how to add it on an app-by-app basis or enable it system-wide.

Got a theory? Know something about this? Drop a comment!