With nearly three billion monthly active users, Facebook remains one of the top destinations on the web and makes money by targeting its users with ads based on their behavior. But few people are aware of how expansively Facebook tracks users when they are not on Facebook—whether they’re Facebook users or not.

Facebook offers an invisible tracking tool, called a pixel, that websites across the internet can embed to enable much of that tracking. 

The pixel is a snippet of code that, once installed on a webpage, sends data to Facebook as people visit. When you view content on some pages, type in your payment information, or buy something, pages with Facebook pixel installed can then transmit that information to Facebook, which can then use the data to target advertisements. Websites add the code to their pages in hopes of better targeting their products and services on Facebook to potentially interested customers.

This tracking can happen even to internet users who don’t have a Facebook account, and it’s pervasive. Blacklight, our real-time web privacy inspector, has found that more than 30 percent of popular websites have Facebook pixel encoded. In response to congressional questioning in 2018, Facebook said more than two million of its pixels were installed on websites.

But while Facebook’s privacy practices have led to historic fines and (largely stalled) legislative proposals, the scope of the pixel’s use is yet to be fully understood. We want to learn more about how and where Facebook pixel is tracking web users. 

So we are excited to announce our “Facebook Pixel Hunt” study. In partnership with Mozilla Rally, the Pixel Hunt is a reader-powered project that looks to uncover what data Facebook is quietly collecting as people browse the web.

If you are a Firefox user, you can help us investigate the Facebook pixel: The more data we have, the more we can explore. Here’s how to help.

Step 1: Install the Mozilla Rally browser add-on

To participate, you will need to install the Mozilla Rally add-on:

• First, visit Mozilla Rally’s website from your Firefox browser.
• On the top right of the Mozilla Rally page, click on the “Install Rally for Firefox” button.
• Mozilla Rally will start installing automatically. You will see a pop-up that asks for permission to allow the extension to access your data. Click “Add.”
• When you have completed these steps, the Mozilla Rally installation is complete. You will see the Mozilla Rally flag icon in the top of your browser toolbar.

Step 2: Complete the setup

Once you install the add-on, you can review the Mozilla Rally Privacy Notice and complete a brief demographic survey that includes your age, gender, race/ethnicity, education level, household income, and zip code. The survey is optional.

Step 3: Sign up for our Facebook Pixel study

Now that you have the Mozilla Rally add-on installed, you can enroll in our study. 

• After completing or declining the demographic survey, you will be directed to the “Current Studies” page. You can also access this page anytime by clicking on the Mozilla Rally flag icon in your browser toolbar.
• You will see our study, “Facebook Pixel Hunt,” featuring the bright pink Markup logo. 
• From here, all you need to do is click on the blue “Join Study” button at the top of the information card.
• You will see a screen with a brief introduction and instructions for when you are ready to leave the study. Click “Accept & Enroll.”
• The Mozilla Rally add-on will automatically update, and a pop-up will ask for permission to access data and browser activity. Click “Add.”
• Your toolbar will introduce a pop-up saying the “Facebook Pixel Hunt” was added. Close this window, and you are all set.

Once you have Mozilla Rally installed, there are other studies that run on Rally that you can participate in as well. 

Researchers at Stanford GSB are studying online news consumption, and researchers at Princeton are looking at search engine data as well as how political and COVID-19-related news is spread online. You will see all these studies listed on Mozilla Rally’s “Current Studies” page, which is accessible once you have the Mozilla Rally add-on installed.

Mozilla Rally collects:

• Your demographic data from the optional survey.
• Your device’s technical data, including operating system and IP address. Your IP address is only stored temporarily.
• Your interactions with Firefox, including the number and type of Firefox add-ons you have installed, your interactions with the Rally add-on itself, and the duration of your active browsing session.
• Your location data, including your country, city, and state location, which is determined by your IP address.
• The URLs of the webpages you visit and the time you spend on those pages.
• The presence of Facebook log-in cookies in your browser.
• The data sent to Facebook by Facebook pixel as you browse the web. (Form data is hashed by Facebook so we cannot see passwords, etc.)
• Mozilla encrypts all collected data until it is transferred to their secure analysis environment. 
• Mozilla takes extensive measures to protect participants’ privacy, and it only collects the data it informs you about—nothing more.

Mozilla only shares with us the data that we need to analyze the data sent to Facebook pixel as you browse using Firefox. This includes the URLs of the webpages you visit, the time you spend browsing pages, and the presence of Facebook log-in cookies in your browser. The Markup will access this data in Mozilla’s secure server environment. Data we use for reporting will be aggregated and anonymized.

We will be collecting data until July 13, 2022, and publishing stories around our findings in the coming months. You can leave the study at any time by simply clicking the Rally button in your Firefox toolbar and selecting “Leave Study.”

We hope you can join us. We are excited to share what we find.