All platforms with Thunderbird: The gContactSync add-on synchronises your contacts between Gmail and Thunderbird's address book. While gContactSync syncs email addresses without a hitch, it is a little fussier about the formatting of the street address fields. If you're a Thunderbird power user with a large set of Gmail contacts to import and synchronise, it's definitely worth the inconvenience of tweaking your Gmail contacts. Fortunately there's a video walk-through available to guide you through the needed tweaks, when you go to the download page at mozdev.org, a link to the flash tutorial is on the right hand side of the screen. gContactSync is a free download and works with Thunderbird.