But what the companies meant was that Yahoo won't send some types of behaviorally targeted ads to Firefox users who have turned on do-not-track. “We will honor third party ad personalization opt-out for Firefox users as part of this partnership,” a Yahoo spokesperson said in response to MediaPost's questions about how the company intends to implement do-not-track for Firefox users.
But Yahoo isn't promising that it will stop collecting data about those Firefox users -- even though data collection is what many privacy advocates find most objectionable about tracking.
The concept of do-not-track, first floated in 2007, has never been fully fleshed out. But the original idea was to offer consumers a simple, persistent mechanism for expressing a preference about online privacy.
Even though online companies and industry groups have long offered people links where they can opt out of receiving behaviorally targeted ads -- that is, ads targeted based on information collected across sites -- those links are cookie-based. When users delete their cookies, they also clear the opt-out links.
Browser headers, by contrast, are persistent. They're also sent to all publishers and ad networks, regardless of whether they participate in an industry-sponsored opt-out program.
Several years ago, the major browser companies began offering a do-not-track setting. But those headers have never prevented online ad companies from gathering data about users or sending them ads. Instead, the headers send a signal to publishers and ad networks -- which are free to honor them or not.
For now, most online ad networks and publishers appear to ignore the signals, with a few notable exceptions, including Twitter and Pinterest. One reason is that the industry hasn't yet decided how to interpret do-not-track requests, even though the Internet standards organization World Wide Web Consortium has been trying to figure that out for more than three years.
Earlier this year, that group (which includes Yahoo and Mozilla representatives) tentatively decided that a “do not track” request will communicate that users don't want data about themselves collected by ad networks. (Despite the proposed definition, the organization anticipates that ad networks will be able to comply with the do-not-track standard and still collect certain types of data about users.)
For its part, this deal isn't Yahoo's first experience with do-not-track. Two years ago, the company said it would stop sending customized ads and content to people who activate browser-based do-not-track settings.
This May, the company abruptly switched gears. “We fundamentally believe the best Web is a personalized one,” Yahoo said in a blog post at the time.