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