All,
Red Hat released the source code for Firefox 38. We have (or willbe today) releasing this for CentOS-5, CentOS-6, and CentOS-7.
It does not, by default, connect to https sites with TLS less than 1.2. This means it will not connect to sites on CentOS-5, for example .. there are many others.
In any event, here is a wiki article that explains potential issues and workarounds:
http://wiki.centos.org/TipsAndTricks/Firefox38onCentOS
Thanks, Johnny Hughes