The Mozilla organization has released a new version, 3.5.4, of the Firefox Web browser. This release fixes eleven security issues, six of them rated Critical. It also incorporates other miscellaneous bug fixes and stability improvements. It is available via the built-in update mechanism (main menu: Help / Check for Updates); alternatively, versions for all platforms — Mac OS-X, Windows, and Linux — are available in 70+ languages from the download page. There’s more information in the Release Notes.
Update Friday, October 30, 23:59
If you are still using an older 3.0.x version of Firefox, there is a new version 3.0.15 which incorporates the security updates. More information is in the Release Notes for Firefox 3.0; versions for different platforms and languages at the download page. Firefox 3.0.x will continue to receive security updates only until January 2010; I suggest you plan to upgrade to the 3.5.x version as soon as it’s convenient to do so.