RPM of new major version of the browser are available in the remi repository for fedora and enterprise linux (RHEL, CentOS, ...).
To read: Mozilla Firefox Release Notes
Installation :
yum --enablerepo=remi update firefox
Notice : this RPM is close of firefox 8 one from fedora 15/16.
This package needs xulrunner8 which install beside default one.
RPM are available for fedora 12 to 14 and, for the first time, for enterprise linux 6...