RPM of new major version of the Mozilla Foundation browser are available in the remi repository for Fedora 16, 17 and Enterprise Linux 6 (RHEL, CentOS, ...).
To read: Mozilla Firefox Release NotesInstallation :
yum --enablerepo=remi update firefox
Notice : this RPM is very close of Firefox 23 one from Fedora 18/19.
This package needs xulrunner-last which install beside default one.
For Enterprise Linux 6, the build use python2.7 available as a SoftwareCollection. (only for build, unneeded at run time).
RPM are available for Fedora 14, 15 (x86_64), 16 et 17 and, for Enterprise Linux 6.