You can remove all data stored in Firefox for a specific domain via "Forget About This Site" in the right-click context menu of an history entry ("History -> Show All History" or "View -> Sidebar -> History"). Using "Forget About This Site" will remove all data stored in Firefox for this domain like history and cookies and passwords and exceptions and cache, so be careful. If you have a password or other data for that domain that you do not want to lose, make sure to backup this data or make a note. You can't recover from this 'forget' unless you have a backup of involved files. If you revisit a 'forgotten' website, data for that website will be saved once again. *https://support.mozilla.org/en-US/kb/delete-browsing-search-download-history-firefox ---- Start Firefox in <b>Troubleshoot Mode</b> to check if one of the extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) or if <b>hardware acceleration</b> or if <b>userChrome.css/userContent.css</b> is causing the problem. *switch to the Default System theme: "3-bar" menu button or Tools -> Add-ons -> Themes *do NOT click the "Refresh Firefox" button on the Troubleshoot Mode start window *https://support.mozilla.org/en-US/kb/diagnose-firefox-issues-using-troubleshoot-mode *https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems You can check the connection settings and check for possible issues with a Proxy or VPN service. *Settings -> General -> Network: Connection -> Settings If you do not need to use a Proxy to connect to internet, select "No Proxy" if "Use the system proxy settings" or one of the others do not work properly. See also: *https://support.mozilla.org/en-US/kb/connection-settings-firefox *https://support.mozilla.org/en-US/kb/websites-dont-load-troubleshoot-and-fix-errors