Firefox 63, out today, includes the first iteration of what Mozilla is calling Enhanced Tracking Protection (ETP), a feature to improve privacy and stop your activity across the Web from being tracked.

Tracking cookies store some kind of unique identifier that represents your browser. The cookie is tied to a third-party domain—the domain of the tracking company, rather than the site you're visiting. Each site you visit that embeds the tracking cookie will allow the tracking company to see the sites you visit and, using that unique identifier, cross-reference different visits to different sites to build a picture of your online behavior.

Firefox has long had the ability to block all third-party cookies, but this is a crude solution, and many sites will break if all third-party cookies are prohibited. The new EPT option works as a more selective block on tracking cookies; third-party cookies still work in general, but those that are known to belong to tracking companies are blocked. For the most part, sites will retain their full functionality, just without undermining privacy at the same time.

At least for now, however, Mozilla is defaulting this feature to off, so the company can get a better idea of the impact it has on the Web. In testing, the company has found the occasional site that breaks when tracking cookies are blocked. Over the next few months, Firefox developers will get a better picture of just how much breaks, and, if it's not too severe, the plan is to block trackers by default starting in early 2019.

If a site is broken by having tracking cookies disabled, Firefox also includes an ability to override the block on a per-site basis.

A second privacy-related feature may be a little more contentious. Starting from tomorrow, a random selection of US Firefox users will be offered a subscription to ProtonVPN. VPNs provide protection and privacy from network eavesdroppers and have become particularly popular by users of public Wi-Fi hotspots in cafes, airports, hotels, and so on.

The unusual feature is that ProtonVPN is a paid service. ProtonVPN is offering a $10/month subscription to Firefox users, with a portion of that subscription fee going to Mozilla. Mozilla is currently heavily dependent on money from Google; Google pays a large sum of money to have its search engine as the Firefox default. This is an unusual relationship, given that Firefox directly competes with Google's Chrome. Mozilla is hoping that this VPN promotion will enable it to broaden its revenue sources, making it less dependent on Google's cash.