Like most browsers, Firefox has the ability to remember passwords you enter for various sites. On most browsers, this creates a security hole. Once someone has access to your computer they can see all of your passwords. Firefox has a nice feature in that you can set a master password that limits access to seeing the passwords that you have entered. To set this, get to the Security tab in Preferences and check the box called "Use a master password". If you are having Firefox remember passwords and you do not have this box checked, you have a huge security hole on your computer.