OK but needs major improvement Rated 2 out of 5 stars
Works pretty good. I have had the duplicate items issue a couple of times with no explanation. The good part is that google adds contacts created in Thunderbird to your "other contacts" folder and does not add them to "my contacts". Therefore, you can go to google and delete all of your "other contacts" and get rid of all the duplicates. There is one major flaw in this process. If you have added other contacts from Thunderbird it will delete those too. I am still using this for a while to see if it can be fixed but at this point it's pretty sketchy. MAKE A BACKUP OF YOUR CONTACTS!
Also, it doesn't seem to sync with google until you exit and restart the program.