Mozilla has become the latest developer to add an optional 'privacy' feature to its web browser.

Nicknamed 'porn mode' the feature prevents the browser from downloading cookies or writing to the browser's cache or web history.

The option is already available in Apple's Safari and Google's Chrome. Microsoft plans to implement it in the upcoming version of Internet Explorer.

Aside from hiding the user's less-savoury browsing habits, the feature also aids security in some situations.

Users of public computers which may be shared with strangers can use the setting to prevent others from seeing items such as bank web sites visited or other potentially sensitive information.

The privacy browsing mode is set to debut in the beta versions of Firefox 3.1 scheduled for release some time next month.