It's not so bad Rated 4 out of 5 stars

I'd like to respond to some of the comments. The installation is kind of weird but the instructions are correct! Right click and save the install file. Then select tools->add-ons from the thunderbird program to install the calendar. Secondly, the calendar gadget can easily be hidden. Simply grab the horizontal bar between the folder selections and the calendar and drag it toward the bottom and the calendar gadget will disappear. When you want it back, grab the bar at the bottom and pull it back up.

This review is for a previous version of the add-on (0.5).