RPM of new major version of the Mozilla Foundation browser are available in the remi repository for fedora 14, 15 and enterprise linux 6 (RHEL, CentOS, ...).
To read: Mozilla Firefox Release NotesInstallation :
yum --enablerepo=remi update firefox
Notice : this RPM is close of firefox 16 one from fedora 16/17/18.
This package needs xulrunner15 which install beside default one.
RPM are available for fedora 14, 15 and, for enterprise linux 6.