Review for Google Contacts by PeterVermont
Rated 5 out of 5 stars
my current version: 0.4.20.
I have been using this for a while. In the past I have had some problems losing groups. Just now however, working in gmail, I renamed some groups, created some, deleted some and also deleted a bunch of 'suggested contacts'. I then re-opened Thunderbird and it worked perfectly.
To create your own collections, you must have a Mozilla Add-ons account.