Mozilla Firefox (3.5 onwards) has a cool feature that can allow one to surf the internet even on a shared computer and leave no trace behind (history, cookies etc). This is called Private Browsing feature and is useful when a single login id is being used to access Firefox and other applications on a computer. It can be enabled by simply hitting Ctrl + Shift + P or through Tools > Start Private Browsing. (For security and privacy reasons however, if one is using a shared computer with say other family members or so it is best to have different user accounts on same computer rather than use a single account for everyone).
However this will only make the Private browsing feature visible by showing the status as Private Browsing in Firefox title bar . In order to launch this Private Browsing mode automatically each time Firefox is launched and not display the status as Private Browsing in the title bar, do the following :
1. Go to Preferences and select Privacy tab.
2. Select Use custom settings for history from the first drop down box.
3. Enable the check mark next to Automatically start Firefox in a private browsing session option.
Restart Firefox and from now on you will be using the Private Browsing mode each time Firefox is launched.
Happy and safe surfing.