This can be caused by corrupted cookies or cookies that aren't send or otherwise blocked. *https://support.mozilla.org/kb/fix-login-issues-on-websites-require-passwords Clear the cache and the cookies from sites that cause problems. "Clear the Cache": *Tools > Options > Advanced > Network > Cached Web Content: "Clear Now" "Remove Cookies" from sites causing problems: *Tools > Options > Privacy > Cookies: "Show Cookies" ----- Please Update to the latest Firefox 18.0.x version. *Help > About Firefox *https://support.mozilla.org/kb/update-firefox-latest-version *https://support.mozilla.com/kb/Updating+Firefox The Firefox Firefox 15.0.1 version that you currently run is no longer supported with security updates