Review for Google Contacts by Matthew Derrick
Rated 4 out of 5 stars
Despite what others say, this extension is still working for me. I've tested creating contacts as well as deleting them, and they all sync both ways.
The only thing that confuses me is that this page lists the latest version as 0.7.12 and the date of release as June 20, 2013.
Inside thunderbird, it's listed as 0.7.12 with a release date of December 24th, 2013. So I dunno if there was a patch released that fixed other folk's problems, but like I said, it's working for me.
I'm also using Thunderbird 24.2.0.
To create your own collections, you must have a Mozilla Add-ons account.