"Mozilla has completed work on its private browsing mode, the feature the organisation delayed the launch of 3.1 to implement. Private browsing mode allows users to surf the web without leaving any traces of their session on the computer. The company was initially reluctant to include the feature, putting it on hold for four years.
The privacy mode will appear in Firefox 3.1 beta 2 due for release by the end of the month. It is also available in the nightly builds for anybody who wants to try it out sooner." – Content courtesy of PC Pro: News: Firefox 3.1 passes major milestone