Privacy mode or "private browsing", sometimes informally referred to as "porn mode", is a term that refers to privacy features in some web browsers. Historically speaking, web browsers store information such as browsing history, images, videos and text within cache. In contrast, privacy mode can be enabled so that the browser does not store this information for selected browsing sessions. This allows a person to browse the Web without storing local data that could be retrieved at a later date. It is of note that this offers virtually no privacy protection beyond the local level. For example, it is still possible to identify frequented websites by associating the IP address with the user on the server end. Privacy mode will also disable the storage of data in cookies or Flash cookies.

The Mozilla Foundation made a study about the user behavior when the feature is switched on and how long the session lasts. The results were that most sessions last only about 10 minutes, though there are periods where activation increases; usually around 11 a.m. to 2 p.m., 5 p.m., between 9 p.m. and 10 p.m., and a minor peak about an hour or two after midnight.