The Firebug extension is probably worth looking at here, as it has a button to open the interface in a popup window (which is more or less the same thing, and this would enable that possibility as well).
I think this can be done by abstracting the existing overlay slightly and overlaying it on a placeholder in both the browser window and an independent XUL file.
Some code would have to be adjusted to handle the different contexts, but I believe it should be possible.
Targeting to 1.1 as a major feature
