Mozilla on Tuesday rolled out the eleventh beta of Firefox 4, adding the "Do Not Track" feature it touted three weeks ago to the browser.
The open-source company plans one more beta, which it hopes to wrap up this weekend, before moving on to "release candidate" builds that in turn will lead to final code.
Mozilla has said it will ship a completed Firefox 4 this month.
The privacy feature, announced Jan. 23 , lets users opt out of the online tracking conducted by Web sites and advertisers. When users enable the feature in Firefox 4 Beta 11, the browser transmits special information with every HTTP page request, telling the site that the user does not want to be tracked.
However, the information Firefox sends as part of each HTTP header won't change how advertisers track users until sites and advertisers modify code on their end to respond to the Do Not Track request. Mozilla made that clear in a blog post announcing the availability of Firefox 4 Beta 11.
"You will not notice any difference in your browsing experience until sites and advertisers start responding to the header," said Mozilla.
Mozilla's approach differs from that taken by rivals Microsoft and Google, which have also revealed no-tracking plans.
Microsoft's Internet Explorer 9 (IE9) will include what the company has called "Tracking Protection," an opt-in tool that relies on published lists to selectively block third-party sites and content embedded in Web sites.
IE9 Release Candidate, or RC -- the last preview of the browser -- will launch later today with Tracking Protection.
Google, meanwhile, has launched the "Keep My Opt-Outs" add-on for Chrome that leverages self-regulation efforts by the online advertising industry to let users permanently opt out of ad tracking from participating companies.
The San Francisco-based Electronic Freedom Foundation (EFF) has thrown its weight behind Firefox's strategy, saying that it has a "clear lead" over rivals in the Do Not Track race.
"We believe that the only sensible way forward for privacy opt-outs is a Do Not Track header, and we're very pleased to see Mozilla planning to offer this option in their future browser versions," Rainey Reitman, EFF's activism director, said in a January blog post .
Mozilla plans to roll out one more beta for Firefox 4, but has not set a schedule, saying only that it hoped to quash all remaining blocker bugs -- the problems that would prevent it releasing Beta 12 -- by tomorrow, then close the code over the weekend.
At one point Mozilla had slated only 10 betas, but the company added another pair to the schedule as it wrestled with bugs.
Firefox 4 Beta 11 can be downloaded for Windows, Mac OS X and Linux from Mozilla's Web site.