Rated 3 out of 5 stars

Can't get it to shutdown Ubuntu 10.10 w/FF 6.0.1. To use the sudo shutdown command the user's password is required. Anyone get this to work please post here what you did.

This review is for a previous version of the add-on (0.7.1-signed). 

Have you tried the predefined shutdown command (with ConsoleKit) for Linux?
If it's not working try the following command (maybe ConsoleKit is not present in Maverick):
Executable: /usr/bin/dbus-send
Arguments: --print-reply --dest=org.gnome.SessionManager /org/gnome/SessionManager org.gnome.SessionManager.RequestShutdown
This only works with Gnome.