Clear the cookies for that website. Detail like websites remembering you and log you in automatically is stored in cookies, so you need to clear its cookies to make the website forget about you. *Settings -> Privacy & Security<br>Cookies and Site Data: "Manage Data" ---- *https://support.mozilla.org/en-US/kb/clear-cookies-and-site-data-firefox *https://support.mozilla.org/en-US/kb/how-clear-firefox-cache