1. Open Thunderbird
2. Select the Address Book button in the left menu bar
3. Select Import in the top menu bar
4. Select the file type you have to import
5. Select Continue
6. Locate and select the file you have to import from the pop-up File Explorer or Finder
7. Select Open
8. Select address book fields you want imported
9. Uncheck any address book fields that were automatically checked that you do not want imported
10. Select Continue
11.  Select where you want the data to be put in your Address Book
12. Select Continue
13. Select Start Import
14. Select Finish
    
    Your address book has now been imported into Thunderbird.  

1. Open Thunderbird
2. Select the Address Book button in the left menu bar
3. Select Address Book you want to export the contacts from
4. Select the three more dots next to that Address Book
5. Select Export
6. Select where you want to save the file
7. Name your file and select the file type you wish to save it as in your pop-up File Explorer or Finder window
8. Select Save

You can now use that exported file for another email service.