- With Thunderbird open, click the Address Book button to open your address book.
- Go to Tools > Import.
- Choose Address Books and click the Next button.
- Select Text File (LDIF, .tab, .csv, .txt) and click the Next button
- Select the file of the address book you want to import and click Open. Thunderbird will import the file automatically.
- Click Finish. You should see the new address book you just imported in the list.