CentOS Errata and Bugfix Advisory 2016:0134 

Upstream details at : https://rhn.redhat.com/errata/RHBA-2016-0134.html

The following updated files have been uploaded and are currently 
syncing to the mirrors: ( sha256sum Filename ) 

i386:
732d70ca9a967fcd57ca72070966871c2962d75daf354e353ec62f277ba5e801  firefox-38.6.0-2.el6.centos.i686.rpm

x86_64:
732d70ca9a967fcd57ca72070966871c2962d75daf354e353ec62f277ba5e801  firefox-38.6.0-2.el6.centos.i686.rpm
970b53958a88395b0cdf9564fddcc953669449cfac05cb377b8208718977a78a  firefox-38.6.0-2.el6.centos.x86_64.rpm

Source:
a26f1e526805cef57139007e5fee42e8e0fa1b1aad682337a0a9c56949923598  firefox-38.6.0-2.el6.centos.src.rpm