Working with multiple browser instances using JavaScript

import java.util.Iterator;
import java.util.List;
import java.util.Set;

import org.openqa.selenium.WebDriver;
import org.openqa.selenium.chrome.ChromeDriver;
import org.openqa.selenium.chrome.ChromeDriverService;
import org.openqa.selenium.firefox.FirefoxDriver;
import org.testng.annotations.BeforeTest;
import org.testng.annotations.Test;
import org.openqa.selenium.JavascriptExecutor;

import com.gargoylesoftware.htmlunit.javascript.background.JavaScriptExecutor;

public class Mul_Browser_Instance {
WebDriver d;
//WebDriver d1=new ChromeDriver();
//d1=System.setProperty("webdriver.chrome.driver", "C:\\v2autoW5.0\\Test\\chromedriver\\chromedriver.exe");
//WebDriver actDriver = new ChromeDriver();
@BeforeTest 
public void start(){ 
  d = new FirefoxDriver();
}
 


         @Test 
          public void SearchSuggestion() throws InterruptedException { 
           
  d.get("http://google.com");     
System.out.println("google from FF");
System.out.println(d.getTitle());

Set<String> listoffirstbrowserwindows=d.getWindowHandles();
System.out.println(listoffirstbrowserwindows);
String firsrbrowser=d.getWindowHandle();
System.out.println(d.getTitle());
((JavascriptExecutor)d).executeScript("window.open();");
Set<String> listofsecondbrowserwindows=d.getWindowHandles();
System.out.println(listofsecondbrowserwindows);
listofsecondbrowserwindows.removeAll(listoffirstbrowserwindows);
System.out.println(listofsecondbrowserwindows);
String secondBrowser=((String)listofsecondbrowserwindows.toArray()[0]);
System.out.println(secondBrowser);
d.switchTo().window(secondBrowser);
//System.setProperty("webdriver.chrome.driver", "C:\\v2autoW5.0\\Test\\chromedriver\\chromedriver.exe");
//WebDriver actDriver = new ChromeDriver();
d.get("https://yahoo.com");
Thread.sleep(2000);
d.switchTo().window(firsrbrowser);
Thread.sleep(2000);
d.switchTo().window(secondBrowser);

Thread.sleep(2000);
d.switchTo().window(firsrbrowser);
System.out.println("last aaa");
Thread.sleep(2000);
d.switchTo().window(secondBrowser);
System.out.println("last bbbb");
//System.setProperty("webdriver.chrome.driver", "C:\\v2autoW5.0\\Test\\chromedriver\\chromedriver.exe");
//WebDriver actDriver = new ChromeDriver();
//actDriver.get("https://webmail.in.v2solutions.com/owa");

//actDriver.get("http://yahoo.com");
//System.out.println("yahoo in chrome");
//System.out.println(actDriver.getTitle());


/*Set<String> mumbro=d.getWindowHandles();
Iterator<String> ii=mumbro.iterator();
String pwin = null;
String cwin= null;
while(ii.hasNext())
    {
    d.switchTo().window(pwin);
    System.out.println("now am in parent browser-1");
    }
d.switchTo().window(cwin);
System.out.println("now am in child browser-1");*/
         }

}