Mozilla is responding to challenges from browser rivals Apple, Microsoft and Google by reviving private browsing mode features in Firefox.

The approach has been considered before but was sidelined in the run-up to the release of Firefox 3.0. However, the inclusion of similar privacy protecting features in Apple's Safari and, more recently Google Chrome and IE 8 beta 2, has revived interest in the approach and spurred a decision to incorporate the technology in the first beta of Firefox 3.1, due out next month. The decision was made at a meeting of Mozilla developers on Tuesday.

Private browsing, more memorably described as 'porn mode', makes it easier to hide a user's surfing from others using the same machine. A history of sites visited in this mode is not recorded and cookies are purged at the end of a session. In addition, content isn't cached and passwords entered won't be autosaved. A long discussion between Mozilla developers on how this should work in detail can be found here.

The most obvious application of the technology is visiting risqué sites, but it also has a variety of other uses from surfing for a birthday present for loved ones to researching medical conditions. In a discussion, Mozilla developers highlighted how the approach would make it safer to use shared PCs in libraries and cyber cafés.

Apple's Safari browser and Google Chrome both incorporate a private browsing mode. The second beta of IE, published late last month, saw the debut of Microsoft's version of "privacy mode" browsing. Dubbed "InPrivate Browsing", the feature opens a window that scrubs itself clean when it gets closed.

A Firefox add-on dubbed 'Stealthier' adds similar features, but the time is now thought ripe to include the technology as standard. Private mode browsing features were on the list for Firefox 3.0 but were sidelined in January so that developers could concentrate on ironing out the wrinkles in other technologies thought to be more important at the time, Computerworld adds.

Private browsing features in general are a client-side feature, and irrelevant when considering the tracking technology from the likes of Phorm or plans by government to impose a mandatory data retention regime on ISPs, for example. Various technologies such as Tor provide enhanced privacy, but no absolute guarantees of confidentiality. ®