Review for gContactSync by muthubuntu
Rated 3 out of 5 stars
Having success with the CardDAV protocol instead of any add-ons - does this work for everyone? Add a new address book using CardDAV protocol, then use your gmail username and this url:
https://www.googleapis.com/.well-known/carddav
Taken from this article:
https://developers.google.com/people/carddav
Ultimately found this on a comment on the blog for the gcontactsync blog
To create your own collections, you must have a Mozilla Add-ons account.