Try the steps at [[Websites look wrong or appear differently than they should]]

Usually it is best to first try these basic steps: Reload web page(s) and bypass the cache to refresh possibly outdated or corrupted files. *Press and hold Shift and left-click the Reload button. *Press "Ctrl + F5" or press "Ctrl + Shift + R" (Windows,Linux) *Press "Command + Shift + R" (MAC) *http://en.wikipedia.org/wiki/Wikipedia:Bypass_your_cache ---- 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