Released January 21st, 2010, Firefox 3.6 is built on Mozilla’s Gecko 1.9.2 web rendering platform, this version is also faster and more responsive than previous versions and has been optimized to run on small device operating systems.

Installation for Ubuntu karmic

$ sudo add-apt-repository ppa:ubuntu-mozilla-daily/ppa

$ sudo apt-get update && sudo apt-get install firefox-3.6

Go to Applications > Internet > Namoroka Web Browser to start firefox 3.6.

REF: Firefox 3.6 Release Notes