Java 设置意外警报行为不适用于selenium firefox驱动程序

我需要为firefox设置selenium webdriver的意外警报行为功能。我有以下java代码

package org.openqa.selenium.example;

import org.openqa.selenium.Capabilities;
import org.openqa.selenium.UnexpectedAlertBehaviour;
import org.openqa.selenium.firefox.FirefoxDriver;
import org.openqa.selenium.firefox.FirefoxProfile;
import org.openqa.selenium.remote.*;


public class Example {

public static void main(String[] args)
{
    FirefoxProfile profile = new FirefoxProfile();

    DesiredCapabilities capability = DesiredCapabilities.firefox();
    capability.setCapability(CapabilityType.UNEXPECTED_ALERT_BEHAVIOUR, UnexpectedAlertBehaviour.IGNORE);
    capability.setCapability(FirefoxDriver.PROFILE, profile);

    FirefoxDriver ffDriver = new FirefoxDriver(capability);


    Capabilities actualCap = ((RemoteWebDriver)ffDriver).getCapabilities();

    if(actualCap != null)
    {           
        //inspect unexpected alert behavior
        Object c = actualCap.getCapability(CapabilityType.UNEXPECTED_ALERT_BEHAVIOUR);  

        String capabilityValue = "";
        if(c != null)
        {
            capabilityValue = c.toString();
            System.out.println("Value of capability is " + capabilityValue);
        }
    }
    else
    {
        System.out.println("No capability available!");
    }

    System.out.println("End of app.");
}
}

但这不起作用，我正在使用SeleniumWebDriver v2.37的独立JAR