The folks over at Mozilla have not just been working on Thunderbird. They’ve also released a new version, 3.6.11, of the Firefox Web browser, for Windows, Linux, and Mac OS X. The new version fixes several stability-related bugs, and also incorporates fixes for ten security vulnerabilities. Further information on the changes is in the Release Notes.
I recommend that you install this update as soon as you conveniently can. You can get the new version via the built-in update mechanism (Menu: Help / Check for Updates); alternatively, you can download an installation package, available in many (human) languages.