Many US hospitals' and clinics' web sites give data about patients and their medical conditions to Facebook.

Tracking tokens are especially dangerous when they send medical information, but they are always an injustice. They ought to be prohibited in all web sites, or even better, blocked from functioning. I use a browser, IceCat, which blocks tracking tokens in a very general way by blocking third-party resources.

Some plug-ins for Firefox also block tracking tokens.