There are two default address books in Thunderbird. The Personal and the Collected. These cannot be removed. The Personal is for most of the uses and is the default when addressing using the address books. This is where I suggest that you add your new contacts. An easy way to add an address from an existing email message is to click on the star to the right of an email address in the email header bar. '''This is NOT the same star that shows to the left of the email listing in the Inbox.''' The Collected book picks up all addresses in outbound mails and stores them there. When you import an address book from another application it makes a new book and places those contacts in that book. You can drag and drop contacts between address books to move them or consolidate books. Open the Address Book window and make sure the Directory Pane is turned on and showing. You turn it on from the menu bar by selecting View-Layout-Directory Pane. To move contacts between books select the folder of the book you want to move the contacts '''FROM '''so it displays in the main window. Now select the contact or contacts that you want to move. Drag those selected contacts to the folder of the new book in the Directory Pane and drop them there. When typing contact info into an address field of a new message Thunderbird will look in ALL the address books for matches. Another helpful option when addressing a new mail is to turn on the Contact Sidebar in the Write window. Open a Write window Press F9 to turn on the Contact Sidebar. This will show the Personal book by default but there is a drop down list of all books so you can change the one displaying.