Following the release of Firefox 10.0.1 on Friday, the Mozilla organization has released version 10.0.1 of its Thunderbird E-mail client, for Windows, Mac OS X, and Linux. This new version of Thunderbird fixes the same Critical vulnerability fixed in Firefox 10.0.1, and also incorporates some other bug fixes. More details are available in the Release Notes.
Because of its security content, I recommend updating your system to the new version as soon as you conveniently can. You can get the new version via the built-in update mechanism (Help / About Thunderbird / Check for Updates), or you can download an installation package in a variety of languages.