To get the latest Thunderbird just update the OS or download it from Softpedia
Canonical published in a security notice details about Thunderbird vulnerabilities for its Ubuntu 12.04 LTS, Ubuntu 11.10, Ubuntu 11.04, and Ubuntu 10.04 LTS operating systems.According to Canonical, several security issues were fixed in Mozilla Thunderbird. It was discovered that the Thuderbird contained several memory corruption flaws, improperly handled the <select> element, did not properly follow the HTML5 specifications, did not properly perform security checks on test methods for DOMWindowUtils, and allowed improper access to the Location object
The security flaws can be fixed if you upgrade your system(s) to the latest Thunderbid, specific to each operating system. To apply the update, run the Update Manager application.
In general, a standard system update will make all the necessary changes. A system restart won't be necessary to implement the changes.
Alternatively, you can download Mozilla Thunderbird 16.0.1 right now from Softpedia.