Does this problem occur every single time you close Firefox and start it again, or only when you shut down Windows and start Windows up again? There are two ways that you could stay logged in to the Yahoo website from session to session: (1) Let Firefox keep cookies, and have Yahoo set a cookie (normally you see a checkbox when you login). By default, Firefox will keep cookies as long as websites request. However, that may be changed by (A) modifying privacy settings (see: [[Websites say cookies are blocked - Unblock them]]), or (B) installing add-ons that modify how cookies work, or (C) using external software that cleans up browser settings. (2) Use Firefox's password manager to save the login and log you in. Websites frequently try to evade the password manager by changing how their forms work, so this could stop working based on a site redesign. More info on the password manager: [[Password Manager - Remember, delete, change and import saved passwords in Firefox]]. If the problem only occurs at Windows startup, check to see whether you have a program like CCleaner set to remove browser data at system startup.