STEAREL  Works as advertised... once. However, when I press "done" and enter a new string of html code and press "Tidy It!" the results shown are the same as the first entry.

For example, if I tidy up the source code from apple.com and then try to tidy up the source code from google.com, the results for apple.com shows up again.

Logging out and logging back in resets the problem to allow one successful Tidy operation.

Great idea. Keep going with it. I would also suggest a graphic interface with check boxes and drop down menus on the back side of the widget.  
(Version 1.0)