org.openqa.selenium.ElementNotInteractableException: Element is not reachable by keyboard: while sending text to FirstName field in Facebook

The error is :

Exception in thread "main" org.openqa.selenium.ElementNotInteractableException: Element is not reachable by keyboard

System.setProperty("webdriver.gecko.driver","//Users//rozali//Documents//Selenium//geckodriver");
        WebDriver driver = new FirefoxDriver();
        driver.get("http://www.facebook.com");
        driver.manage().window().maximize();

        //entering first name
        driver.findElement(By.id("u_0_b")).click();
        driver.findElement(By.id("u_0_b")).sendKeys("testing it ");
        
        //DOB
        Select sel1 = new Select(driver.findElement(By.xpath(".//*[@id='month']")));
        sel1.selectByIndex(4);
        
        Select sel2 = new Select(driver.findElement(By.xpath(".//*[@id='day']")));
        sel2.selectByValue("6");
        
        Select sel3 = new Select(driver.findElement(By.xpath(".//*[@id='year']")));
        sel3.selectByValue("2013");
        
        //clicking sign up
        driver.findElement(By.id("u_0_t")).click();