在调用后 driver.close（）驱动器的值设置为

After calling driver.close() the value of driver is set to

FirefoxDriver: firefox on WINDOWS(4b4ffb1e-7c02-4d9c-b37b-310c771492ac)

但如果你调用 driver.quit（）然后设置驱动器，以

FirefoxDriver: firefox on WINDOWS (null)

所以，如果你调用后检查浏览器窗口中的 driver.quit（）的，那么你就可以通过下面的实施就知道了。

So if you're checking the browser window after calling driver.quit() then you will be able to know by below implementation.

WebDriver driver = new FirefoxDriver();
driver.get("http://www.google.com");
driver.quit();              
if(driver.toString().contains("null"))
{

System.out.print("All Browser windows are closed ");
}
else
{
//open a new Browser
}