A silly little hack I devised this afternoon if you run Gnome 3 and have the pretty (but unused) Contacts icon in your Applications menu. Open this as root:

/usr/share/applications/mozilla-seamonkey.desktop

And replace this:

Exec=gnome-contacts

With this:

Exec=seamonkey -addressbook

One of these days I'll fulfill my dream of writing an entirely XUL desktop environment. And it'll use the Walnut theme by default. Oh, you'd better believe it.