Move failing Firefox spec into guarded block.
Move failing Firefox spec into guarded block.

There's a regression in selenium-webdriver >= 2.35.1, where drag-and-drop now fails not only when the *draggable* is outside the viewport, but also when the *droppable* is outside the viewport
See https://code.google.com/p/selenium/issues/detail?id=3075#c33

watir/watirspec,titusfortner/watirspec,titusfortner/watirspec,titusfortner/watirspec,watir/watirspec,watir/watirspec