How to set menu bar with child window in javafx?

       vbox2.setPadding(new Insets(3));
        vbox2.setSpacing(3);
         vbox2.getChildren().addAll( browser1,browser);

        HBox.setHgrow(vbox2, Priority.ALWAYS);


        hbox.setPadding(new Insets(20));
//        StackPane.setMargin(hbox, new Insets(20));
        hbox.getChildren().addAll(vbox, vbox2);
        root.getChildren().add(hbox);
        Scene scene = new Scene(root, 500, 300); // the stack pane is the root node
        //scene.setCursor(Cursor.CROSSHAIR);
           MenuBar menuBar = new MenuBar();
             Menu menu = new Menu("Window");
        menu.getItems().add(new MenuItem("browser"));
        menu.getItems().add(new MenuItem("img"));
        menuBar.getMenus().add(menu); 
         menuBar.prefWidthProperty().bind(primaryStage.widthProperty());
    BorderPane borderPane = new BorderPane();

        borderPane.prefHeightProperty().bind(scene.heightProperty());
        borderPane.prefWidthProperty().bind(scene.widthProperty());

        borderPane.setTop(menuBar);
           root.getChildren().add(borderPane);
        primaryStage.setScene(scene);
        primaryStage.show(); 
    }

here is the code part where is im adding menu bar with border pane but its hang my application as im not able to login or do anythng and i had to add child window also for reference im attaching the image

This is a very basic and minimal example of handling views in the center of a BorderPane by MenuItems:

import javafx.application.Application;
import javafx.stage.Stage;
import javafx.scene.Scene;
import javafx.scene.control.Label;
import javafx.scene.control.Menu;
import javafx.scene.control.MenuBar;
import javafx.scene.control.MenuItem;
import javafx.scene.layout.BorderPane;
import javafx.scene.web.WebEngine;
import javafx.scene.web.WebView;

public class Main extends Application {
    @Override
    public void start(Stage primaryStage) {
        try {
            BorderPane root = new BorderPane();
            // create the menu bar with a menu and its items
            MenuBar menuBar = new MenuBar();
            Menu mainMenu = new Menu("Window");
            MenuItem browserItem = new MenuItem("browser");
            MenuItem imageItem = new MenuItem("image");
            MenuItem closeItem = new MenuItem("exit");
            // create some different contents for the center of the border pane
            Label imagePlaceHolder = new Label("IMAGE TO BE SHOWN");
            WebView browser = new WebView();
            WebEngine browserEngine = browser.getEngine();

            // set the actions for the different items
            closeItem.setOnAction(action -> {
                System.exit(0);
            });

            imageItem.setOnAction(action -> {
                root.setCenter(imagePlaceHolder);
            });

            browserItem.setOnAction(action -> {
                root.setCenter(browser);
                browserEngine.load("http://www.google.com");
            });

            // add items to the menu, then the menu to the menu bar
            mainMenu.getItems().addAll(closeItem, browserItem, imageItem);
            menuBar.getMenus().add(mainMenu);

            // set the scene
            Scene scene = new Scene(root,400,400);
            root.setTop(menuBar);
            primaryStage.setScene(scene);
            primaryStage.show();
        } catch(Exception e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) {
        launch(args);
    }
}

I hope it helps…

EDIT I just saw your newest edit… In case you really need different windows (scenes or stages), the approach will get more complex. Readers have to get more information about the different windows (like how you create them, handle their contents and more).