Your antivirus software is attempting to intercept communications between NamePros and your browser. However, when it re-encrypts the information it retrieves, it uses an insecure encryption configuration that Firefox no longer allows. Chrome will soon be disallowing it as well. I don't know the specifics of how Avast works, but I do know that the method it's using here is quite controversial, and I would not personally trust my personal information with such software.
There isn't anything NamePros can do about this. You will need to either contact Avast or switch antivirus suites.