Wikimedia Bugzilla is closed!

Three repos (Echo, Flow, MobileFrontend) are using this step: 

Given(/^I am using user agent "(.+)"$/) do |user_agent|
  @user_agent = user_agent
  @browser = browser(test_name(@scenario), {user_agent: user_agent})
  $session_id = @browser.driver.instance_variable_get(:@bridge).session_id
end

and doing that properly requires the @custom_browser tag. 

We should move this code into the Ruby gem so it is not repeated among 3 repos. 

Also, more repos will probably be testing no-javascript mode in the future, so this would likely see even more re-use. 

Finally, the shared code should throw an error if BROWSER is anything other than Firefox