The Facebook Pixel Hunt aims to unravel Facebook’s tracking methods. Will you join?

The Facebook Pixel Hunt aims to unravel Facebook’s tracking methods. Will you join?

Browser developer Mozilla has announced a research project to provide insights into, and data about, a space that’s opaque to policymakers, researchers and users themselves. Tracking the trackers is the name of the game. Give up some of your data voluntarily to stop the involuntary collection by Facebook.

Mozilla is partnering with The Markup, with the aim of unravelling how Facebook’s tracking infrastructure massively collects data about people online. Data which is eventually used for targeted advertising and tailored content recommendations.

Firefox users will get the option to participate in the project dubbed “the Facebook Pixel Hunt” and volunteer to share their browser data.

What is The Markup?

The Markup is a non-profit organization that investigates how powerful institutions are using technology to change our society. The Markup is the latest partner for Rally, the privacy-first data-sharing platform that was created by Mozilla in 2021 to take back control from platforms that are not transparent about how they use people’s data. When they hide their methods, the platforms make it very difficult for independent outside research to take place.

Just a few examples: Facebook shut down CrowdTangle, blocked ProPublica’s Ad Transparency tools, modified code to prevent The Markup’s Citizen Browser from collecting user-volunteered data and canceled NYU’s AdObserver researchers’ accounts.

The research project

Using tools provided by Rally, the two organizations will research how Facebook tracks people across the web through its Facebook pixel-powered ad network, and shine a light on what Facebook knows about their online life.

The Facebook pixel is a piece of code that website owners can place on their website. The pixel collects data that helps businesses track conversions from Facebook ads, optimize ads, build targeted audiences for future ads, and remarket to people that have already taken some kind of action on their website. That’s nice for the advertisers, but the combined information of all these pixels potentially provides Facebook with an almost complete picture of your browsing behavior.

By opting into “the Facebook Pixel Hunt” study, Rally gives Firefox users the power to help answer questions like: What kind of data does the Facebook pixel collect? Which sites share this data? What can this data reveal about people? What other ways does Facebook track people? How widespread is Facebook’s tracking network?

To answer these questions the study will collect:

  • The data sent to Facebook pixels as you browse
  • The (full) URLs of the web pages you browse
  • The time you spend browsing pages and time spent browsing and playing media on each webpage
  • The presence of Facebook login cookies in your browser
  • Metadata on the URLs your visit, like how far down the webpage you scrolled
  • A study survey that you complete, the results of which will be combined with study data for the analysis

Who can join?

If you want to contribute to this study there are a few things to check. Participation in the study is currently available for Firefox users in the US who are 19 or older. Having a Facebook account is not mandatory. Facebook may collect information about you across the web even if you don’t have a Facebook account.

If you decide to leave the study, Mozilla Rally uninstalls the corresponding study add-on. If the study is still open, the data that the study collected will be deleted. If a study has already ended, it may not be possible to delete your data because deletion of the data may impact the ability of the partners in the study to do their research.

How can I participate?

Taking part in the study is as easy as installing a browser add-on for Firefox. You can find the Rally add-on here. After installing you will see this explanatory page:

Mozilla Rally

And this flag icon in your browser bar:

Rally icon

For demographic reasons you will be asked a few questions, although answering them is optional. The answers will help the researchers understand the representivity and diversity of the users.

You can then choose which study you want to participate in.

Facebook Pixel Hunt study

After joining the study you will notice another extension in Firefox.

Firefox extensions

Users of Malwarebytes Browser Guard for Firefox that wish to participate in this study will have to disable Browser Guard or, recommended, add to their allow list for Ads/Trackers.

Here’s how to add an entry to the allow list for Malwarebytes Browser Guard:

  • Click the Malwarebytes icon in the browser bar
  • Click the 3 dots icon
  • Select Allow list
  • Add “” in the “Add a URL or IP address” field
  • Select Ads/Trackers in the “Disable protections” field
  • Click “Done”

After successfully adding the entry, the allow list should look like this:

allow list

Other add-blockers may require additional actions for users to be helpful in this study.

We are looking forward to the results and hope that Facebook will not try to frustrate this study as well.


Pieter Arntz

Malware Intelligence Researcher

Was a Microsoft MVP in consumer security for 12 years running. Can speak four languages. Smells of rich mahogany and leather-bound books.