Import Your Gmail Contacts into Mozilla Thunderbird

To export your address book from Gmail and import it into Mozilla Thunderbird:

• Save your Gmail contacts as gmail-to-outlook.csv.
• Select Tools | Import... from the menu in Mozilla Thunderbird.
• Make sure Address Books is selected.
• Click Next >.
• Highlight Text file (LDIF,.tab,.csv,.txt) under Please select the program from which you would like to import.
• Click Next >.
• Select the gmail-to-outlook.csv file you just created.
• Make sure First record contains field names is checked.
• Use the Move Up and Move Down buttons to match Mozilla Thunderbird address book fields on the left with Gmail fields on the right.
  • Make sure at least
  • Primary Email and E-mail Address and
  • Last Name and Name match.
  • Gmail has a unified name field and does not distinguish between first and last names.
  • You can use the Next button at the top to see what the import process will produce.
• Click OK.
• Now click Finish.

In your Mozilla Thunderbird address book, you will now find a folder named "gmail-to-outlook" with all imported contacts.

Source