gcontactsync is an extension that synchronizes contacts from a Google (Gmail) account with an Address Book in Thunderbird 2 or 3 written for a Google Summer of Code project in 2008.
The code is at version 0.1.1. It is a little buggy and runs rough, but with a little TLC it does a good job of syncing up GMail and Thunderbird. IT is far better than the Zindus plugin, which missing syncing up a lot of fields in the contacts.
For Mac users, its pretty easy to get a copy of your Mac address book into Thunderbird by exporting it to vcard format, then converting to LDIF for import to Thunderbird. Thunderbird 3 will display your Mac address book directly into Thunderbird (I’m told)
There is a handy tutorial flash for installing and using the extension, as well as the extension’s xpi link, here.
[...] Beta it’s contacts are integrated with the Mac OS X Address Book as well. That makes this extension for syncing Thunderbird 2.0 with GMail Contacts sort of redundant, except that it does a periodic sync in the background. Apple’s iSync [...]