No it's not. You have to enter your website URL into the developer page for your app. When Facebook login is called it checks to make sure that the website you are logging in from is the "approved" website. But by running from preview, the website you are sending to Facebook is local host rather then myapp.com so it generates an error and won't let you log in. It's a nice safety feature that keeps other people from stealing your app and cloning it to do malicious things under your Facebook Id( the Id set as the app owner)