What is a web tracker?

Let’s say you’re on an outdoor pizza oven website dreaming about someday owning one. Mmm pizza. Next you switch gears and visit a fitness site; lo and behold an ad for the pizza oven you were just looking at is there, too. Then you go to YouTube to see how easy it would be to build your own pizza oven (it’s too hard), but first you have to sit through an advertisement about, you guessed it, that same pizza oven. Time to check Instagram on your phone, and there it is again, grinning at you as a sponsored post in your feed.

It’s not just a feeling. That ad really is following you and it happens all the time. So how do these sites all know exactly how to tempt you to a point of annoyance? Is it magic? Nope. The answer is web trackers.

What exactly is a web tracker?

Generally, a tracker is a script on websites designed to derive data points about your preferences and who you are as you interact with their site. Sometimes these scripts are placed purposefully by the website you’re on, other times a script may be from a website you’ve never visited. Understanding the ways your data is collected can help you limit your exposure to trackers in the future.

Types of web trackers


These are a commonly used method to track you as you browse the web. Cookies are small pieces of data saved to your browser by websites. Every time you visit a web page, cookies can be stored on your device. But not all cookies are created equal. The website that you are visiting may have its own cookies, called first-party cookies, which are placed to suggest content that is most relevant for you, help you remember your log ins, prevent fraud, and more.  

Super cookies

A super cookie is a browser cookie that can be permanently stored on your computer. Super cookies are harder to detect and get rid of because they can’t be auto-deleted the same way as regular cookies. By injecting super cookies into your device, websites can access your personal information, behavior and preferences. Super cookies can also track the time you’re most active on the internet. This next-level data is a goldmine for advertisers who can use the information to create targeted ads based on user profiling and preferences.

Embedded scripts

There are a variety of tracking resources that can be embedded as visible or invisible elements on a page. Common examples are pixel trackers that are clear images embedded on a web page or email; or tracking scripts that run as you visit websites and can do a number of things to track you, from recording your IP address to capturing your device’s specifications.


Fingerprinting scripts scrape data from your web browser, including your browser’s type and version, your device’s operating system and version, your screen resolution, installed fonts and can even see all the apps you’ve downloaded on your device. This data is assembled into a fingerprint unique to your device and can be used to distinctly track you across websites.

Third-party trackers are bad

Third-party trackers are placed by a website you haven’t even visited. They come from separate entities — sometimes vast ad networks — you’ve never heard of and almost certainly didn’t agree to share your information with. These third parties are able to place trackers on sites across the web, thereby collecting tons of data about you and sharing it with whomever they want. Yah, it’s kind of creepy.

You can stop web trackers

It’s not all doom and gloom. At Firefox we believe you have a right to privacy and to choose what information you share about yourself. That’s why we block third-party tracking cookies by default in Firefox browsers. If you want even stronger protection, you can take advantage of Firefox’s full tracker blocking capabilities by setting your Enhanced Tracking Protection mode to Strict to help block these other trackers, like fingerprinters. Additionally, we offer Facebook Container, the free browser extension that blocks Facebook from tracking your movements across the web when you’re logged in.

There’s much more to be learned about web trackers than what’s in this article. For more reading, check out this article about Social Trackers.

This post is also available in: Deutsch (German) Français (French)

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