Über dieses Add-on
This extension was originally created as a workaround for bug #177175.
You may cancel the password prompt by default. This is not a bug.
It is impossible to secure your account by installing an extension, because extensions can be disabled easily, e.g. by running the application in safe mode. If you understand the security concerns and still insist, you may force the application to quit on cancel by enabling the relevant option in the extension settings.
Uninstalling the add-on does not clear the master password.
You won't get a password prompt at startup, but Firefox will still ask your password when you first visit a site with stored credentials. Thunderbird will ask you when downloading new mail. If you would like to disable this protection altogether, be sure to change your master password to an empty one before uninstalling StartupMaster.