title: How to run a method before all tests in all classes?
body: <p>I'm writing selenium tests, with a set of classes, each class containing several tests.  Each class currently opens and then closes Firefox, which has two consequences:</p>
  
  <ul>
  <li>super slow, opening firefox takes longer than running the test in a class...</li>
  <li>crashes, because after firefox has been closed, trying to reopen it really quickly, from selenium, results in an 'Error 54'</li>
  </ul>
  
  <p>I could solve the error 54, probably, by adding a sleep, but it would still be super slow.</p>
  
  <p>So, what I'd like to do is reuse the same Firefox instances across <em>all</em> test classes.  Which means I need to run a method before all test classes, and another method after all test classes.  So, 'setup_class' and 'teardown_class' are not sufficient.</p>