I have recently had a lot of “This web page is trying to open an app outside of Facebook. Are you sure you want to open it?” dialog boxes when viewing outside links in the Facebook app. I usually tap cancel, but when I let it go through, It tries to invoke an outside app, and goes to the app store if it’s not available.
It is normal for the App Store to pop up when you tap on an ad, but this is occurring before the page has even finished loading. Best I can figure is that someone has discovered a new Javascript trick that invokes the app in Facebook’s browser. I have not seen that behavior in Safari.
That is a JAVA script function. . . and some Ad companies have figured out how to call it. The App Store has a URL, so it is fairly easy to call it, but it supposed to be intentional, not automatic. MacDailyNews ad server was doing that and they were trying to find a way to block it from their website. It appears to be inherent in HTML5.