selenium-webdriver 3.4.0, firefox-53.0.2, geckodriver-v0.16.1-linux64.tar.gz
https://github.com/mozilla/geckodriver/releases
geckodriver-v0.16.1-linux64.tar.gz
$ unzip geckodriver_geckodriver-v0.16.1-linux64.tar.gz
$ sudo mv geckodriver /usr/bin/
$ cd /usr/bin
$ sudo chmod +x geckodriver
Ruby
Selenium::WebDriver::Firefox.path ='~/firefox-53.0.2/firefox'