Mozilla released a major update for Thunderbird on July 22nd, 2014 with version 31.0. Information about this release can be viewed here. Depending on the users update settings, they will be prompted to install the Thunderbird Update or may do so via Help > About Thunderbird. Users can also download and manually install the latest version of Mozilla Thunderbird via getthunderbird.com site.,
The next scheduled update for Thunderbird will be in about six-weeks with Thunderbird 31.1.0 on September 2nd, 2014.