Nice find Dan. Handy little extension that's very useful and has been working fine on Minefield (3.0a3pre) for me for a little while now.
Either the author or AMO have restricted it to work between versions 2.0 to 2.0.0.* so I've bumped this copy of
Permatabs 1.4.0 to work on Bon Echo, Minefield and Gran Paradiso as well. It won't work on 1.5.* though. Left click to install and right click to download.
Cheers