If you do not need to use a proxy to connect to internet then try to select "No Proxy" if "Use the system proxy settings" or one of the others do not work properly. See "Firefox connection settings":
Oct 02, 2014 How to Fix Server Not Found Error on Firefox – Jaxsonharry Disable Temporarily Firewall and Anti-Virus. The Window Protector Anti-virus and firewall program … Fix: Secure Connection Failed PR_END_OF_FILE_ERROR on Firefox Apr 15, 2020
How to fix the problem of server not found in Firefox
Firefox will send your browsing activity through the proxy server running on your local computer. By default, Firefox uses SOCKS v5 for the connection. Select SOCKS v4 if your SOCKS proxy uses the older standard instead. If you’re not sure, leave the option set to SOCKS v5. Jan 03, 2011 · We all use Mozilla Firefox and the common problem which has been encountered with recently is with the message Server Not Found. It’s not because of No Internet connectivity or Low speed internet connectivity but was due to some other reasons, so let’s check out the reasons on why it sometime shows Server Not found?
Firefox is a Web browser which gives users a cleaner interface and faster download speeds but there are problems like Firefox can't find server or unable to connect so t fix it you must make sure your modem and/or router are both on and not indicating errors,if using a wireless connection make sure you are connected to the right access point,your Internet security software is not blocking
Dec 14, 2010 web-browsers - "server not found" in firefox [SOLVED Server not found. Firefox can't find the server at