RPM of the new version of messaging client is available in remi for fedora ≤ 12 (backport of F-13 version).
Start by reading :
Thunderbird Release Notes
As always:
yum --enablerepo=remi update thunderbird
enigmail (version 1.1.2) and lightning (version 1.0b2pre) extensions are also available.
RPM are availalble for fedora ≥ 8. This version will also be available in official
updates for F-13... thunderbird-3.1.2