Setting the cookie mf_useformat ensures that the mobile site gets loaded.
If tests are run against en.m. etc.. this won't have any effect, but a
lot of local instances are setup to run the desktop URL by default. An
alternative way of doing this would be to toggle to the mobile site
explicitly in the test suite.

e.g.
Given /^I am in the mobile view$/ do
  on(ArticlePage).switch_to_mobile_element.click
end

In terms of 2nd question - no I don't think we should abandon trying
to test Nearby in the browser, it is one of our most important
features and has extremely inadequate test coverage and is one of the
things that seems to break the most. Even if the test only works for
Firefox, having that test is a good thing.