How to Sync Thunderbird Contacts with Gmail Contacts

Solution 1:

I'd recommend the Google Contacts add-on for Thunderbird (update 2015: this is no longer supported or available for recent versions of Thunderbird >24.X)

Access bi-directionaly to Google contacts via address books. This extension 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.

For more information, click this link.

Solution 2:

I've tried a few (including Zindus), and have settled on gContactSync: https://addons.mozilla.org/en-US/thunderbird/addon/8451

Can't say how it compares to Google Contacts in particular, but I'm using gContactSync on three PCs, and syncing my Google contacts with my iPhone, and am very happy.