ubuntu ruby firefox selenium-webdriver-3.14.1
https://libraries.io/rubygems/selenium-webdriver
~/.rvm/gems/ruby-2.5.1/gems/selenium-webdriver-3.14.1/lib/selenium/webdriver/common/service.rb:57:in `binary_path': Unable to find Mozilla geckodriver. Please download the server from https://github.com/mozilla/geckodriver/releases and place it somewhere on your PATH. More info at https://developer.mozilla.org/en-US/docs/Mozilla/QA/Marionette/WebDriver. (Selenium::WebDriver::Error::WebDriverError)
https://github.com/mozilla/geckodriver/releases
$ sudo mv geckodriver /usr/bin/geckodriver
$ sudo chown root:root /usr/bin/geckodriver
$ sudo chmod +x /usr/bin/geckodriver