To fight Apple’s privacy protection Facebook, Instagram et al have found a way to track everything you do, by drawing you into their in-app browser and then injecting a surveillance Javascript. If you want to see what they actually do, just forward a link to InAppBrowser.com within the app and click it.
Introducing InAppBrowser.com, a simple tool to list the JavaScript commands executed by the iOS app rendering the page.
With Android, don’t even bother.