I think they figured out that adult sites are going to be browsed. So they built in a feature that I think is very handy for surfing adult sites without leaving a footprint on your PC.
You can read more about Firefox 3.5's Private Browsing here: http://support.mozilla.com/en-US/kb/...mode=inproduct
download it here:
http://en-us.www.mozilla.com/en-US/
note: If you are on a corporate network or use a dialup provided by your company, the company may still be able to monitor your web browsing. Some companies are furnished usage reports on their corporate ISP accounts.