Rated 4 out of 5 stars

Good, Add-on, but there is one Problem.
Google now support hd pictures up to 720x720px.
So they are synched to Android as well in this resolution.
No I found out, that some of my pictures were scalled back to 96x96px. The Cause for this is the synching with TB. There the pictures are dwonsized. I don't know if this is a problem of TB adresse book or the add-on. But there could be the option to turn off picture syncing. Then the Problem would not exist.

This review is for a previous version of the add-on (0.3.6). 

gContactSync downloads photos from Google and does not scale them. Thunderbird is responsible for displaying the photos.

gContactSync has a preference to not download photos. Go to Menu -> Options -> Options -> Advanced -> Config Editor. Type "photos" in the textbox and change getPhotos and setPhotos to false.