Looks that some CSS files are blocked. If you use extensions ("3-bar" menu button or Tools > Add-ons > Extensions) that can block content (e.g. Adblock Plus, NoScript, Flash Block, Ghostery) then make sure such extensions do not block content. There is security software that can interfere with loading content, so check that as well. *https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes There is security software like Avast and Kaspersky and BitDefender and ESET that intercepts secure connections and sends their own certificate or that incorporates special web shielding features that can block content. *https://support.mozilla.org/kb/troubleshoot-SEC_ERROR_UNKNOWN_ISSUER You can check the log in the Web Console for error messages and the Network Monitor (Firefox/Tools > Web Developer) to see if content fails to load or is possibly blocked. *https://developer.mozilla.org/Tools/Web_Console *https://developer.mozilla.org/Tools/Network_Monitor Use Ctrl+F5 or Ctrl+Shift+R to reload the page and bypass the cache to generate a fresh log.