I recently installed Testing Framework.  I installed the chrome extension by dragging and dropping the file onto a chrome://extensions window.  (Chrome 35) After a few minutes of trying to run tests, I noticed that the extension was disabled and could not be re-enabled.  

I installed telerik's Chrome Inspector, Chrome Recorder, and Chrome Playback from the Google Web Store, and now I'm getting the following for a test that only opens one URL and counts the number of "table" tags it finds.
System.AppDomainUnloadedException: Attempted to access an unloaded AppDomain. This can happen if the test(s) started a thread but did not stop it. Make sure that all the threads started by the test(s) are stopped before completion.