In addition to the release of Firefox 19.0 yesterday, Mozilla has released version 17.0.3 of its Thunderbird E-mail client, for Linux, Mac OS X, and Windows. This release corrects eight security vulnerabilities, four of which are rated Critical. (These are the same vulnerabilities that were fixed in Firefox 19.0. The two packages share a significant amount of code.) A bug with handling attachments in the message composition window was also fixed. More information is available in the Release Notes.
Because of the security fixes incorporated in this release, I recommend that you update your systems as soon as you conveniently can. You can use the update mechanism built into the software (Help / About Thunderbird / Check for Updates), or you can get a complete installation package, in a variety of languages, from the Thunderbird download page.