RPM of the new major version of Mozilla Foundation messaging client is available in remi for fedora (backport of rawhide version).
As this is a new major version, a backup of your profiles seems mandatory (.thunderbird folder) Start by reading : Thunderbird Release Notes As always: yum --enablerepo=remi update thunderbird enigmail (version 1.1.1) and lightning (version 1.0b2pre) extensions are also available. A annoying issue with this version requires to register... Lire Thunderbird 3.1