Firefox doesn't know how to communicate with server

Problem:
Unexpected response from server
Firefox doesn't know how to communicate with server

• Check to make sure your system has Personal Security Manager installed.
• This might be due to a non-standard configuration on the server.

Why?
When you upgrade Firefox from an older version to version 1.5.0.7 this might happen.

How to fix it?
Open up a terminal and ...
$ yum update nss
$ yum remove firefox
$ yum -y install firefox