Rated 4 out of 5 stars

Works perfectly! Adds, or rather corrects something which you would expect to find in ThunderBird by default.

@Arty2:
In FireFox, the only use of the master password is to protect the other passwords. The FF version of this add-on basically extends that use to have it restrict access to the program itself. You are right that this is easily circumvented.

In ThunderBird, the master password is used by default to restrict access to the entire program. You can't circumvent it, even if you would disable this add-on.

This review is for a previous version of the add-on (1.6.1-signed.1-signed).