Mozilla did face a real privacy complaint in the European Union—but the case was about Firefox’s experimental Privacy-Preserving Attribution (PPA) system, not evidence that Firefox uploaded users’ complete browsing histories.
Privacy group noyb filed the complaint with Austria’s data-protection authority on September 25, 2024. The complaint alleged that a Firefox setting for privacy-preserving ad measurement was enabled without adequate notice or consent. Mozilla later said PPA was never activated, and its current documentation says the feature was removed. noyb’s case page still lists the complaint as pending.
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What the complaint was about
noyb—short for “None of Your Business”—represented the complainant under Article 80(1) of the GDPR. The complaint, identified as case C089, named Mozilla Corporation as the respondent and was filed with Austria’s Data Protection Authority on September 25, 2024. It cited GDPR provisions covering lawful processing, transparency, information duties and the right to lodge a complaint. Read the complaint.
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Scan for outdated or missing drivers - takes under a minuteDriver Scan →Repair Windows errors before they cause bigger problemsFix Now →Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →The dispute concerned a Firefox option labelled “Allow websites to perform privacy-preserving ad measurement.” According to noyb’s complaint, the complainant found the option enabled in Firefox 128 settings on July 17, 2024, despite not turning it on or receiving adequate information about it.
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That is noyb’s account of what the user saw—not a final finding by a regulator. Mozilla’s later support documentation gives a different description: it says PPA was an experimental Firefox 128 feature that was never activated and was subsequently removed.
What Privacy-Preserving Attribution was supposed to do
PPA was designed to measure whether an advertisement led to an action, such as visiting a website or completing a conversion, without giving advertisers a user’s detailed browsing history.
That makes it different from conventional cross-site tracking, which can use cookies, pixels or persistent identifiers to build records connected to an individual. Attribution asks a narrower question: did an ad campaign produce a result?
Mozilla’s proposed PPA flow was broadly as follows:
- A website asks Firefox to record that an advertisement was viewed.
- Firefox stores limited impression information locally.
- If a later conversion occurs, the destination website asks the browser to create a report.
- Firefox encrypts and splits the report.
- Aggregation services combine reports from multiple users.
- Differential-privacy techniques add statistical noise before aggregate results are provided to an advertiser.
Mozilla said the prototype was intended to reduce reliance on invasive advertising systems, not to enable individual ad targeting. Its proposed initial test was limited to Mozilla-operated websites, including Mozilla VPN advertising on MDN. The company described protections involving encryption, the Distributed Aggregation Protocol, an Oblivious HTTP relay to obscure IP addresses, aggregation and differential privacy. Mozilla’s technical explanation is available here.
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Why noyb objected
noyb’s objection was not simply that Firefox contained an advertising-related feature. Its argument was that moving measurement into the browser does not automatically stop it from being tracking or make the underlying processing lawful.
- Default activation: noyb alleged that the setting was enabled without the user’s affirmative action.
- Notice and transparency: it argued that users were not properly informed about the feature or its operation.
- Legal basis: the complaint questioned whether Mozilla had a valid GDPR basis for the processing and whether consent requirements had been met.
- Control of the measurement system: noyb argued that browser-mediated measurement could still amount to tracking from the user’s perspective, even if it used privacy-enhancing technology.
- Anonymization: noyb challenged the assumption that encryption, aggregation or pseudonymization automatically makes the resulting information anonymous for GDPR purposes.
The distinction matters. A system can reduce the amount of information available to advertisers while still processing information on a user’s device. “Privacy-preserving” describes a design goal and a set of safeguards; it does not by itself resolve every question about consent, transparency or GDPR applicability.
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What Mozilla said
Mozilla presented PPA as an alternative to more invasive forms of cross-site advertising measurement. Its position was that no single party would receive a complete, readable report tied to an individual user. Reports would be protected, divided between aggregation parties and combined only in aggregate.
Mozilla also said the prototype would be tightly limited: it was intended for an origin trial involving Mozilla-operated sites rather than an open system available to advertisers across the web. The company’s design included IP-address protection through an Oblivious HTTP relay and differential privacy to make it harder to infer a specific person’s activity from aggregate results.
Those are technical and policy claims about how PPA was designed. They should not be confused with the separate factual question of whether the feature was activated in practice. The complaint records a user-visible setting that noyb said was enabled; Mozilla’s later help page says PPA was never activated. The available material does not independently establish that Firefox generated or transmitted PPA reports from ordinary users.
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Was Firefox sending users’ browsing histories?
There is no support in the available record for saying that PPA sent users’ complete browsing histories to Mozilla or advertisers.
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Mozilla’s description concerned limited ad-impression and conversion information, not a complete log of every site a person visited. Firefox’s privacy documentation also generally describes browsing history and similar information as being processed on the device unless the relevant notice says otherwise. That does not settle the legal debate over PPA, but it does rule out the stronger claim that this complaint demonstrated wholesale uploading or sale of browsing histories.
It is also inaccurate to describe PPA as proven cookie replacement. Mozilla presented it as a possible alternative to more invasive measurement, while noyb argued that it could become an additional measurement route rather than replacing existing tracking technologies.
What happened after the complaint
| Date | Event |
|---|---|
| July 17, 2024 | The complainant said they found the ad-measurement option enabled in Firefox settings. |
| Firefox 128 | PPA-related code and settings were associated with this release. |
| August 22, 2024 | Mozilla published its explanation of the PPA prototype. |
| September 25, 2024 | noyb filed the GDPR complaint with Austria’s data-protection authority. |
| October 18, 2024 | The authority forwarded the complaint to Mozilla, according to noyb’s case log. |
| November 6, 2024 | noyb recorded Mozilla’s submission that it did not process data. |
| November 19, 2025 | Mozilla’s support documentation was updated to describe PPA as a historical feature that was never activated and was removed. |
| August 18, 2026 | noyb’s case page still listed the complaint as pending, with an expected processing period of 18–24 months. |
The noyb case page does not report a final Austrian data-protection decision. Accordingly, the available record does not establish that Mozilla violated the GDPR, nor does it show that the EU fined or ruled against Mozilla.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Does PPA still exist in Firefox?
According to Mozilla’s current support documentation, no. PPA was an experimental Firefox 128 feature, was never activated, and was later removed. It should not be presented as a currently operating Firefox tracking system.
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This later documentation is the most important update to older coverage. The original complaint remains relevant because it raised questions about default settings, notice and the legal treatment of browser-based ad measurement. But it does not show that PPA is still running on current Firefox installations.
What current Firefox controls are separate from PPA?
Firefox has other controls relating to technical data, interaction data, sponsored content and New Tab features. These should not be labelled PPA or treated as proof that PPA survived its removal.
On desktop, Mozilla’s documented path for the relevant data-sharing control is:
- Open the Firefox menu and select Settings.
- Choose Privacy & Security.
- Scroll to Firefox data collection and use.
- Uncheck “Allow Firefox to send technical and interaction data to Mozilla.”
This control concerns current Firefox data-collection practices; it is not a PPA switch. Mozilla’s current Firefox Privacy Notice also describes controls for New Tab features and sponsored content, along with privacy technologies such as aggregation, de-identification, Oblivious HTTP and the Distributed Aggregation Protocol.
What the case does—and does not—show
The complaint highlights a genuine policy problem: privacy-enhancing advertising measurement can still raise questions about what a browser records, who controls the process, what users are told and whether the legal basis is sufficient.
But the evidence supports a narrower conclusion than headlines such as “Firefox secretly tracked users” suggest. noyb filed a real complaint over an allegedly enabled setting. Mozilla defended the proposed design and later said PPA was never activated. Its support documentation says the feature was removed, and noyb’s case page continues to list the matter as pending.
So this is a dispute over consent, transparency and the legal status of privacy-preserving ad attribution—not proof that Firefox routinely uploaded users’ full browsing histories.
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