I got to know that using Selenium 3.5.0 + geckodriver 0.16.1 with either Firefox 53.0.3 or 54.0.1 worked for me. I have not tried any older version of Firefox or geckodriver. Also, geckodriver 0.17.0 showed the same behavior as 0.18.0 - It showed "crashing Firefox on RemoteWebDriver.Close()"