RPM of the new version of Mozilla Foundation messaging client is available in remi for fedora 14 and enterprise linux 6 (RHEL, CentOS, ...). This is a backport of F-17 version.
Start by reading : Thunderbird Release Notes As always: yum --enablerepo=remi update thunderbird\* enigmail (version 1.4.1) extension are also available. lightning is no more available. RPM of version 12.0 are availalble for fedora 14, and for enterprise linux 6.... Lire Thunderbird 12