Mozilla acknowledges it may never fully win the ongoing battle against advertisers as the company faces criticism for a new feature in Firefox 128. This feature, which is enabled by default, collects aggregate data on user interactions with ads and shares it with advertisers. Although users can disable this feature, the decision to make it opt-out has sparked significant backlash.
According to Bobby Holley, Chief Technology Officer (CTO) of Firefox, the company should have communicated better about the introduction of “privacy-preserving ad metrics.” In an extensive response on Reddit, Holley explains that while Mozilla has historically aimed to combat online surveillance through anti-tracking measures, these efforts face two major limitations.
First, the economic incentives for advertisers to bypass these countermeasures are immense, creating a perpetual arms race that Mozilla might not win. “In the absence of alternatives, there are huge economic incentives for advertisers to circumvent these countermeasures, leading to a permanent arms race that we may not be able to win,” Holley states. Second, these anti-tracking measures only benefit Firefox users, whereas Mozilla aims to enhance privacy for everyone.
Holley notes that most users typically accept the default settings they are given. This tendency undermines the effectiveness of privacy measures that rely on individual responsibility and consent. “Framing the problem as one of individual responsibility is a great way to appease knowledgeable users while ensuring that most people’s privacy remains compromised. Cookie banners are a good example of where this kind of thinking leads,” he says.
According to Holley, Mozilla’s decision not to display a consent screen for this feature was intentional to avoid user distraction. He admits that explaining “privacy-preserving ad measurement” to the average user is challenging, making it difficult for them to make informed decisions.
The controversy centers on the Privacy-Preserving Attribution Measurement API, which Mozilla is developing in collaboration with Meta and other entities. This API aims to measure ad-driven conversions—such as whether a user who saw an ad eventually made a purchase—without using intrusive tracking methods. The system uses a Multi-Party Computation (MPC) system called DAP/Prio, operated in partnership with ISRG.
Holley defends the ad measurement within the browser, stating that digital advertising is an enduring economic model. “Whatever opinion you may have of advertising as an economic model, it’s a powerful industry that’s not going to pack up and go away. A mechanism for advertisers to accomplish their goals in a way that did not entail gathering a bunch of personal data would be a profound improvement to the Internet we have today,” he explains.
The new feature has been limited to a few test sites and is exclusive to Firefox, as part of an effort to inform ongoing technical work. Mozilla argues that a truly private attribution mechanism could eventually eliminate the need for invasive tracking, enabling stricter regulatory action against companies that persist with such practices. “Digital advertising isn’t going away, but the surveillance part can eventually go away if we do it right,” Holley concludes.
While the feature aims to strike a balance between privacy and the economic realities of online advertising, the decision to enable it by default has left many users feeling betrayed by a company traditionally known for its strong privacy stance.
