Rated 4 out of 5 stars

Overall a great addon. I use it at work to keep people from being places they shouldn't. I knock 1 star from it because every other day or so it will seem to forget what the MP is and ask for a new one to be created at start-up. This is an issue because it could allow some people a chance to change the MP and gain access to the places that they shouldn't be. Maybe I'm missing something in the settings, but I haven't run across anything dealing with a password reset/expire.

*I'm curious to figure out why it asks for a new MP to be entered every morning when I start up FF.*

This review is for a previous version of the add-on (1.15.1-signed). 

Neither this addon, nor Firefox/Thunderbird itself has ability "forget" master password without user's interaction. The password itself not being stored on the computer, because of that the only way to remove it (at least known to me) is either using MP remove feature, which asks for MP or delete whole profile