Selenium doesn't explicitly support opening of tabs, however you can do like this:
require 'watir-webdriver'
browser = Watir::Browser.new :ff
browser.goto 'http://the-internet.herokuapp.com'
browser.link(:text, 'A/B Testing').click(:command, :shift)
browser.windows.last.use
This will open the link in a new tab (on a mac) and focus it