Test in anonymous window on Seleniumwebdriver

Question

I’m trying to get Selenium to run the tests in Firefox’s private window, but the execution is still done in the default window. Something is missing?

private IWebDriver driver;
        public IDictionary<string, object> vars { get; private set; }
        private IJavaScriptExecutor js;
        [SetUp]
        public void SetUp()
        {
            driver = new FirefoxDriver();
            FirefoxProfile firefoxProfile = new FirefoxProfile();
            firefoxProfile.SetPreference("browser.privatebrowsing.autostart", true);
            driver.Manage().Window.Maximize();
            js = (IJavaScriptExecutor)driver;
            vars = new Dictionary<string, object>();
        }
        [TearDown]
        protected void TearDown()
        {
            driver.Quit();
        }
        [Test]
        public void teste()
        {
        xxxx
        xxxxx
        xxxxx
        }