Third-party cookies and other trackers
Advertisers want to be sure the money they’re investing is going to the right eyeballs, which is why third-party cookies and trackers have been so important over the last several years. They’re used to identify you and track your activity across the web, which helps advertisers target their ads to the exact demographics they want.
If you want to prevent this, you have to change the cookie privacy settings in your browser. In Firefox, you’ll find these options by navigating to Settings > Privacy & Security > Enhanced Tracking Protection. If you select “Standard,” you’ll get Total Cookie Protection that prevents trackers from following you between sites. For more granular control, select “Custom” and use the drop-down menus to decide what kinds of cookies and trackers you want to block.
Joel Lee / Foundry
However, cookies aren’t the only weapons in an advertiser’s arsenal. They also use something called “fingerprinting,” which combines various data points (like your browser, IP address, time zone, screen resolution, installed software, etc.) to identify who you are. If you want to protect yourself against fingerprinting, you almost have to use the Tor Browser.
Note: You might also notice a “Do not track” option in most browsers. The idea here is that your browser will tell websites and servers that you don’t want to be tracked. However, it’s up to the websites and servers to honor that request — and most don’t, so it’s functionally useless.