https://support.mozilla.org/kb/Clear+Recent+History#w_how-do-i-remove-a-single-website-from-my-history Remove History For One Site Open the History Manager '''<Control><Shift> H.''' In the search bar, enter the name of the site. Right-click on one of the listings and select '''Forget About This Site.''' This should remove all information, including any settings.

Sounds that CSS files are blocked. If you use extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) that can block content (Adblock Plus, NoScript, Disconnect, Ghostery, Privacy Badger, uBlock Origin) always make sure such extensions do not block content. *make sure your extensions and filters are updated to the latest version *https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems Firefox shows the shield icon at the left end of the location/address bar in case Content Blocking is blocking content. *click the shield icon for more details and possibly disable the protection You can check the Web Console about what content is blocked *"3-bar" menu button or Tools -> Web Developer *https://support.mozilla.org/en-US/kb/tracking-protection *https://support.mozilla.org/en-US/kb/content-blocking You can check the Web Console (Tools -> Web Developer) for messages about blocked content and about the presence of mixed or unsafe content. *https://developer.mozilla.org/en-US/Tools/Web_Console You can check the Network Monitor to see if content is blocked or otherwise fails to load. *https://developer.mozilla.org/en-US/Tools/Network_Monitor If necessary use "Ctrl+F5" or "Ctrl+Shift+R" (Mac: Command+Shift+R) to reload the page and bypass the cache to generate a fresh log.