So (if it is ok with you) I would like to break out all of these monolithic tests into multiple tests in the same file that share `setup` and `teardown` logic.

There is a valid performance concern, but if we really need to speed things up in the future, we can build something fancy to run same-file tests in parallel (or just move things to separate files). Also if we run files through marionette-js-runner in parallel in the future, I don't think that not being able to further parallelize these tests will be a huge problem. (I can't imagine a single file taking more than a couple minutes.)