watir firefox install different version
Download target version of firefox
https://ftp.mozilla.org/pub/firefox/releases/
archiving into '~/firefox-42.0/firefox'
(can be checked by ~$:./firefox-42.0/firefox)
Selenium::WebDriver::Firefox.path ='~/firefox-42.0/firefox'
client = Selenium::WebDriver::Remote::Http::Default.new
a=Watir::Browser.new(:firefox, :http_client => client)