How do I debug authentication in Firebase?

Currently, when I set authentication signinflow to redirect, the login process doesn't complete, although it does go to the Google or Facebook login screen. However, when I set the signinflow to popup, the authentication process works as intended. What I'm curious about is how do I go about debugging the authentication in Firebase? The console only shows front-end javascript related code obviously, and the DebugView in the firebase console doesn't show anything when I login or logout whether it's via popup or redirect. What are the steps involved in finding out where the authentication error is in relation to the redirect signinflow mode?

My app.js code is as follows:

firebaseUI.start('#firebaseui-auth-container', {
    signInFlow: 'redirect',
    signInSuccessUrl: 'http://www.bing.com',
    signInOptions: [
      firebaseDB.firebase_.auth.EmailAuthProvider.PROVIDER_ID,
      firebaseDB.firebase_.auth.GoogleAuthProvider.PROVIDER_ID,
      firebaseDB.firebase_.auth.FacebookAuthProvider.PROVIDER_ID
    ],
  });

  firebase.auth().onAuthStateChanged(user => {
    if (user) {
      console.log(user.displayName);
    } else {
      console.log('no user signed in');
    }
  });