Firefox 3.6.6 is ready to download.

What’s New in Firefox 3.6.6
Firefox 3.6.6 modifies the crash protection feature to increase the amount of time that plugins are allowed to be non-responsive before being terminated.

Please see the complete list of changes in this version. You may also be interested in the Firefox 3.6.4 release notes for a list of changes in the previous version.

If you using Ubuntu you can Install or Update it via PPA.

• Open Terminal(Applications – Accessories – Terminal) and copy-paste the following line into Terminal.

  sudo add-apt-repository ppa:ubuntu-mozilla-security/ppa
  

• Done. Now update repositories and upgrade your native Firefox 3.6 to its latest version, Firefox 3.6.6.

  sudo apt-get update && sudo apt-get upgrade

• Done

Source : http://www.techdrivein.com/2010/06/install-or-upgrade-to-firefox-366-in.html