AddOnsFirefox.java

import org.openqa.selenium.firefox.FirefoxProfile;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.remote.DesiredCapabilities;
import org.openqa.selenium.remote.RemoteWebDriver;
import java.io.File;
import java.net.URL;




public class AddOnsFirefox {
	
//======= Set up automate with username and access key=======
  public static final String USERNAME = "<USERNAME>";
  public static final String AUTOMATE_KEY = "<ACCESS_KEY>";
  public static final String URL = "https://" + USERNAME + ":" + AUTOMATE_KEY + "@hub-cloud-us.browserstack.com/wd/hub";
  
  
public static void main(String[] args) throws Exception {
  
//======= Add OS /Browser capabilites=======
	  
    DesiredCapabilities caps = new DesiredCapabilities();
    caps.setCapability("browserName", "Firefox");
    caps.setCapability("browser_version", "45.0");   
    caps.setCapability("os", "Windows");
    caps.setCapability("os_version", "10");

//======= Set the FirefoxProfile to install the extensions =======

   FirefoxProfile firefoxProfile = new FirefoxProfile();   
   firefoxProfile.addExtension(new File("<path to extension>.xpi"));
   caps.setCapability(FirefoxDriver.PROFILE, firefoxProfile);
  

WebDriver driver = new RemoteWebDriver(new URL(URL), caps);
driver.get("http://www.google.com");
Thread.sleep(50000);
driver.quit();
   
}
}