What is NSS error -5961 (PR_CONNECT_RESET_ERROR)

TCP connection reset by peer

This error from NSS is the same error you get with openssl (errno=104: ECONNRESET). This simply means, that the peer or some middlebox in between (firewall) is terminating the connection.

Since the site is reachable from my place I would suggest, that there is a firewall on your site blocking the connection. The behavior is fairly typical for DPI firewalls in that the initial TCP connection is allowed but once you send the first data (ClientHello from TLS handshake) it will determine if your access is allowed by policy and let it pass or deny it by injecting a TCP RST.

yum update curl

solved the problem for me.