When I click the link to the instructions to try a different DNS server (I wonder what “DNS” stands for anyway), I get this:
Server not found
Firefox cant find the server at www.opendns.com.
Check the address for typing errors such as ww.example.com instead of www.example.com
If you are unable to load any pages, check your computers network connection.
If your computer or network is protected by a firewall or proxy, make sure that Firefox is permitted to access the Web.
Taking this to a private post
Mine was similar
DNS DOMAIN NAME SERVER, They maintain a directory of domain names (freerepublic) and translate them to Internet Protocol (IP) addresses (209.157.64.200) which is FRs’ IP address.You may be experiencing a Denial-of-service attack.