Review for Google Contacts by Radical Mike
Rated 4 out of 5 stars
I don't know if this is better than zindus because zindus doesn't work with pre-release versions of Thunderbird, but this extension works great. (I haven't tested one reviewer's claim that offline changes are lost and not synced, but I'll surely keep that in mind.)
This review is for a previous version of the add-on (0.6.10).To create your own collections, you must have a Mozilla Add-ons account.