Mozilla released an update for the Thunderbird 24.x branch on December 10th, 2013. Thunderbird 24.2.0 addressed these issues:

• Security fixes can be found here

• Fixed an issue where long messages with multiple signatures could end up unreadable (bug 929006)

• Fixed an issue where editing account settings was not possible in some non-standard configurations of local folder set-ups (bug 921371)

Depending on update settings, users should automatically be prompted to update to Thunderbird 24.2.0 or may do so manually via Help > About Thunderbird or downloading and installing via the getthunderbird.com site. The next scheduled update will be Thunderbird 24.3.0 on January 21, 2014.