When you sign out of a site, it often will update a cookie on your computer. If you immediately reload the page, it should require you to sign in. If that isn't working correctly, your Twitter cookies might be corrupted. When you have a problem with one particular site, a good "first thing to try" is clearing your Firefox cache and deleting your saved cookies for the site. (1) Bypass Firefox's Cache Use Ctrl+Shift+r to reload the page fresh from the server. (You also can clear Firefox's cache completely using: orange Firefox button ''or'' Tools menu > Options > Advanced On the Network mini-tab > Cached Web Content : "Clear Now") (2) Remove your twitter.com cookies using either of these. While viewing a page on the site: * right-click and choose View Page Info > Security > "View Cookies" * Alt+t (open the classic Tools menu) > Page Info > Security > "View Cookies" Then try reloading the page. Does that help?

See also: *http://kb.mozillazine.org/Cookies *https://support.mozilla.org/kb/Deleting+cookies