Rated 3 out of 5 stars

This is a great product. I keep my thunderbird profile directories shared between Windows and Linux dual boot. If I use the Thunderbird in Windows, it disabled Gcontactsync and after reinstall it works fine. And, when I get back to Linux, I again have to reinstall gcontactsync to make it work again. Needless steps as other extensions work fine in dual boot and shared directory. I would rate 5 star, if this inconvenience did not exist.

This review is for a previous version of the add-on (3.0.0). 

I use it in a dual boot between Windows and Linux on two machines. I suspect the issue is that it is getting disabled because you are using a newer version of Thunderbird than gContactSync v3.0.0 supported. 3.1.4 has support for TB 56 and later.