When do you get that error? Is that t a pop-up alert? Can't you open that website at all or do you still get some content? ---- 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" See also: *https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes