Rated 5 out of 5 stars
I'm using it in Ubuntu Gnome 14.04 with Gnome 3.12.2
I've also have installed fire tray and both extensions work great together. Gnome Integration allows me to have a quick view of the incoming mail and doesn't broke Fire Tray.
Gnome Integration is a high value addition! I think it should come integrated with Thunderbird :P