fixes #4

Author: Nicolas Garnier

src/FirebaseAuth.jsx

@@ -50,7 +50,9 @@ export default class FirebaseAuth extends React.Component {
     const firebaseui = require('firebaseui');
     this.firebaseUiWidget = firebaseui.auth.AuthUI.getInstance()
                           || new firebaseui.auth.AuthUI(this.firebaseAuth);
-    this.firebaseUiWidget.reset();
+    if (this.uiConfig.signInFlow === 'popup') {
+      this.firebaseUiWidget.reset();
+    }
     this.firebaseUiWidget.start('#' + this.elementId, this.uiConfig);
   }