I have added support for running feature tests against FireFox. For that user will have to download gecko driver from https://github.com/mozilla/geckodriver/releases and follow the below steps:
Extract the gecko driver.
Run chmod +x geckodriver.
Either copy the geckodriver to /usr/local/bin or the path of the geckodriver must be specified in PATH.
Apply the attached patch.
Change the parameter "DEFAULT_TEST_BROWSER = 'Firefox' "