Rails automatically disables buttons when submitting a form. This works
fine most of the time: for AJAX requests, it enables them again after
the request is complete, and for non-AJAX requests, the button is
replaced by a new element when the new page loads.
However, there's an exception. When a request returns data so users can
download a fire, the request is not an AJAX one and the button is not
replaced. So users are left with a disabled button they can no longer
click.
So in this case, we aren't disabling the button after a user clicks it.
