...not be static."  This reverts commit
6d4c1f0d.  Whatever made the author of that
commit think rhinoWindow shouldn't be static, it clearly needs to be, as in
edit()'s Runnable.run(), the usage of rhinoWindow at the end relies on
rhinoWindow being set via the

  new ScriptEditorForJavaScript(context, url)

call to initUI() (or else rhinoWindow already being set from a previous such
call if already editor != null).