Mozilla has recently announced a change in our approach to protecting users against tracking. This announcement came as a result of extensive research, both internally and externally, that shows that users are not in control of how their data is used online. In this post, I describe why we’ve chosen to pursue an approach that blocks tracking by default.

People are uncomfortable with the data collection that happens on the web. The actions we take on the web are deeply personal, and yet we have few options to understand and control the data collection that happens on the web. In fact, research has repeatedly shown that the majority of people dislike the collection of personal data for targeted advertising. They report that they find the data collection invasive, creepy, and scary.

The data collected by trackers can create real harm, including enabling divisive political advertising or shaping health insurance companies’ decisions. These are harms we can’t reasonably expect people to anticipate and take steps to avoid. As such, the web lacks an incentive mechanism for companies to compete on privacy.

Opt-in privacy protections have fallen short. Firefox has always offered a baseline set of protections and allowed people to opt into additional privacy features. In parallel, Mozilla worked with industry groups to develop meaningful privacy standards, such as Do Not Track.

These efforts have not been successful. Do Not Track has seen limited adoption by sites, and many of those that initially respected that signal have stopped honoring it. Industry opt-outs don’t always limit data collection and instead only forbid specific uses of the data; past research has shown that people don’t understand this. In addition, research has shown that people rarely take steps to change their default settings — our own data agrees.

Advanced tracking techniques reduce the effectiveness of traditional privacy controls. Many people take steps to protect themselves online, for example, by clearing their browser cookies. In response, some trackers have developed advanced tracking techniques that are able to identify you without the use of cookies. These include browser fingerprinting and the abuse of browser identity and security features for individual identification.

The impact of these techniques isn’t limited to the the website that uses them; the linking of tracking identifiers through “cookie syncing” means that a single tracker which uses an invasive technique can share the information they uncover with other trackers as well.

The features we’ve announced will significantly improve the status quo, but there’s more work to be done. Keep an eye out for future blog posts from us as we continue to improve Firefox’s protections.