Today, Mozilla released a new major version, 12.0, of its Firefox browser for Windows, Linux, and Mac OS X. The new version includes some feature improvements and streamlining; it also fixes 14 identified security vulnerabilities, 7 of which Mozilla rates as Critical. More information about the changes in this version is available inn the Release Notes.
Because of its security content, I do recommend that you upgrade to the new version soon. You can obtain the new version via the built-in update mechanism (Help / About Firefox / Check for Updates), or you can download a complete installation package, in a variety of (human) languages.