Can't turn off Vista Master Password for the software security device

Removing your master password

• Firefox 1.5: "Tools -> Options -> Privacy -> Passwords -> Remove Master Password"
• Firefox 2.0: "Tools -> Options -> Security -> Passwords -> Uncheck "Use a master password". You will be prompted for your Master Password.
• Thunderbird: "Tools -> Options -> Privacy -> Passwords -> Remove Master Password"

If you have lost or forgotten your Master Password or you want to disable the feature, you can reset your master password. Upon resetting, you will lose all the stored information in the Password Manager as this is a built-in security feature to prevent people from simply resetting your Master Password to gaining access to your passwords.
For Firefox you can also look at the Troubleshooting section in Password Manager.

• Firefox: Enter "chrome://pippki/content/resetpassword.xul" in the Location Bar, press Enter, then click "Reset"
• Thunderbird 1.5: "Tools -> Options -> Advanced -> Saved Passwords -> Master Password -> Reset Password".
• Thunderbird 2: Choose Tools – Error Console, paste the expression: openDialog("chrome://pippki/content/resetpassword.xul") and press the Evaluate button. That will open a dialog asking you if you want to reset your password.
• For Mozilla Suite: "Edit -> Preferences -> Privacy & Security -> Master Passwords -> Reset Password".

Taken From MozillaZine, http://kb.mozillazine.org/Master_password

SM