Google Contacts is a Thunderbird add-on which allows you to access your Google contacts and synchronize them with Thunderbird address books. It detects gmail accounts which have already set up and creates address books for each of them.
Cards in the address books are
synchronized with Google contacts; they represent the current Google
contacts contents and Google contacts will be modified when you modify
the cards. TB's mailing lists and Google's contacts groups are
synchronized in the same manner.