How do I stop iTunes from automatically opening when I browse an app on apple.com?
https://gigaom.com/2010/03/15/how-to-stop-itunes-web-links-from-opening-itunes/

It looks like the browser you are using is chrome, so follow these steps


Go to chrome://settings/contentExceptions#javascript
add itunes.apple.com and mark "Block"




If you want to see the app without seeing the "Opening the iTunes Store." page, visit The iTunes Link Maker and see if you can find the app on there. 

(that was my solution before, but it seems now iTunes preview shows the app with a "Opening the iTunes Store." banner. By disabling Javascript on that page, you won't see the banner)