Select Comma Separated Values, then select Next.In the Import and Export Wizard, select Import from another program or file, then select Next.The process of importing is the following: You can manually map columns to fields during the import process. Make sure the columns have meaningful headings, although they don’t have to match exactly the fields used in the Outlook Address Book. In a database or spreadsheet program, export contact data to a CSV (Comma Separated Values) file. After saving the file and closing the prompt in the previous step, you can exit the Address Book window and return to Thunderbird.Click the Save button to export Thunderbird contacts to the folder you selected.However, follow these links to learn more about each format, to find out what it’s used for, how to open it if you end up using it, and more. The CSV format is the most likely format in which it is recommended to save your address book entries.