not exactly tree-view, but it might fit your requirements.

In Mozilla bring up the Address Book by selecting it under the WINDOW menu. If the hot-keys are the same then CTRL-5 should bring it up.

While viewing the address book, choose the FILE menu, NEW sub menu, ADDRESS BOOK option. Give it a name(family, friends, whatever).

I just tried it out, seems to work fine.

Darrell Spice, Jr.                      [link|http://www.spiceware.org/cgi-bin/spa.pl?album=./Artistic%20Overpass|Artistic Overpass]\n[link|http://www.spiceware.org/|SpiceWare] - We don't do Windows, it's too much of a chore