I\'m using Firefox 47.0 with Selenium 2.53. Recently they have been a bug between Selenium and Firefox which make code not working. One of the solution is to use the Marion
You need to specify the system property with the path the .exe when starting the Selenium server node. See also the accepted anwser to Selenium grid with Chrome driver (WebDriverException: The path to the driver executable must be set by the webdriver.chrome.driver system property)