Those folks over at the Mozilla organization have been busy, In addition to the Firefox update yesterday, they also released a new version of the Thunderbird E-mail client, version 3.1.3, for Linux, Mac OS X, and Windows. The new version incorporates bug fixes for the user interface, as well as stability and security updates. (Not surprisingly, many of the security updates are for the same flaws that were patched in Firefox — the two products share a considerable code base.) Further details are in the Release Notes.
I recommend installing this update as soon as you conveniently can. You can get it via the built-in update mechanism (Main menu: Help / Check for Updates), or you can download versions for all platforms and languages here.
Update Thursday, 9 September, 11:18 EDT
Like the recent Firefox 3.6.9 update, this update to Thunderbird fixes the “DLL Hijacking” vulnerability in Windows.