Can you show the issue. Did you try with Firefox in [https://support.mozilla.org/en-US/kb/diagnose-firefox-issues-using-troubleshoot-mode Safe Mode]? You can try to [https://support.mozilla.org/en-US/kb/remove-websites-address-bar-suggestions Clear all items for a single site] You can try [https://support.mozilla.org/en-US/kb/refresh-firefox-reset-add-ons-and-settings Refreshing Firefox].

You can check the connection settings in case you use 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 "Firefox connection settings": *https://support.mozilla.org/en-US/kb/websites-dont-load-troubleshoot-and-fix-errors