Have you just upgraded your Thunderbird email software program? To your horror, the very first thing you may have seen upon closing and opening that program again is that all your email messages and mail boxes have disappeared. Thunderbird email client software needs to convert its database to a new format.
Some time later that computer software program may have asked for your master password. You do not remember ever using a master password and you usually typed individual passwords for each of your accounts. Perhaps you used a master password a long time ago and forgot about it. So what do you do now you ask and how can you retrieve this master password?
You can try removing that master password by typing the following command without quotes into a Microsoft Windows operating system run box C:\path to thunderbird folder\thunderbird.exe -chrome chrome://pippki/content/resetpassword.xul. You will now want to open the Microsoft Windows operating system start button by clicking on Start then select Run and then type in something similar to C:\Program Files\..thunderbird.exe -chrome chrome://pippki/content/resetpassword.xul. The exact command that you will want to type into that Run box is the exact path to your thunderbird.exe file on your computer.
Another option you can try is to delete the C:\Documents and Settings\User\ApplicationData\Thunderbird\Profiles.default/key3.db file from your Mozilla Thunderbird Microsoft Windows operating system profile, which should prompt you to reset that master password when opening up this software program. In that above path user is your Microsoft Windows user name that you are currently logged into that has that password issue. You could also use Microsoft Windows operating system restore tool.
You will want to restore Microsoft Windows operating system back to a point before you upgraded Mozilla Thunderbird software. This time you could go through those Thunderbird settings in order to disable a use of a master password and then try upgrading it again without a master password set. These instructions and tips were written for Microsoft Windows operating system with Mozilla Thunderbird email client software installed.