Facebook is not a walled garden. It is much worse, it is a self contained villages with spiders. One of those spiders leaps on to you. The spider produces a thread that attaches itself to the center Facebook console. When you decide to leave the village the thread and spider go with you. As you go that spider jumps on to other threads that are thrown out by other apps that you visit and ties them to the original thread which sends their information back to Facebook. Apple’s app store privacy crackdownmay cut these threads at least on iOs.