Political microtargeting
Here.
Anybody who spends a lot of time looking at ads coughed up by webpages knows how this works. The defenses against this kind of tracking are not simple, they take time, and are not perfect.
Good starter rule of thumb: deny any website access to your Facebook data. An amazing number of places ask for this to look at games, to comment on news articles, or other things.
The charts in that news article are interesting, and probably worth a study on their own. Still looking through them, but I see some missing options. For example, websites should have included major blogs.