Apple is officially hopping on the "Do Not Track" train, adding support for special opt-out headers in the version of its Safari Web browser set to ship with Mac OS X 10.7 Lion this summer. The feature is already being tested in developer builds of Lion, according to the Wall Street Journal, making Apple the third major browser vendor to support a centralized opt-out mechanism.

The Federal Trade Commission recently called for online advertisers to devise a standard way for consumers to opt out of tracking associated with online behavioral advertising. Instead of the hodgepodge of opt-out mechanisms used for each website or advertiser—if they allow for one at all—the FTC recommended that the industry support a browser-based setting that consumers concerned with privacy could easily set and forget.

Mozilla made the first step in building broad browser support for "Do Not Track" in Firefox 4. Instead of the cookie-based mechanism suggested by the FTC, however, Firefox sends a specially formatted HTTP header to Web servers noting that the user does not want to be tracked. Microsoft added support for the headers in the recently released IE9, and now Apple appears set to add it to Safari once Lion is released.

Mozilla's passive header solution still requires the cooperation of advertisers and social media sites, and the industry has yet to come up with consensus on "Do Not Track." However, Mozilla noted recently that the AP News Registry has implemented support for the DNT header across 800 news sites. That's a proverbial drop in the Internet advertising bucket, but it's a start. And with Safari joining Firefox and IE, 84 percent of the browser market will support "Do Not Track," giving advertisers a big incentive to make use of the system.

If the industry can't or won't get behind the "Do Not Track" initiative, however, it may find itself nudged ahead anyway by proposed consumer privacy legislation from US House Representative Cliff Stearns (R-FL). Stearns intends to offer up an updated version of the Consumer Privacy Protection Act he regionally introduced in 2005, and supports the FTC's authority to monitor privacy practices when it comes to consumer data. The Obama administration supports "Do Not Track" and increased online privacy initiatives, and also endorses using legislation to make it happen. (The Kerry-McCain privacy bill introduced in the Senate contains limits to collecting user information, but doesn't explicitly support "Do Not Track.")

It's worth noting that Google has yet to announce support for Mozilla's DNT headers in its Chrome browser. Google may be reluctant to embrace the standard since it relies heavily on revenue generated from targeted online advertising. However, the company does offer a Chrome plug-in which aims to make it easier to use current cookie-based opt-out mechanisms offered by online advertisers.