So I looked online.
I Google'd "Where is Thunderbird's addressbook"... thinking to find an article telling what file the address book was stored in.
Instead, I found http://kb.mozillazine.org/Run_Address_Book_from_Command_Line
which detailed a different answer --
You can bring up Mozilla Suite's or Thunderbird's Address Book using the command-line switch "-addressbook" [1].
Peace.