Rated 5 out of 5 stars

Works great now, version 0.5.7.1 is out:

http://www.longfocus.com/firefox/gmanager/releases/gmanager0571.xpi

To install, just drag the .xpl file in the Firefox window and it will install itself.

This review is for a previous version of the add-on (0.5.7.1).