have a look at my toy: http://meta.wikimedia.org/wiki/WYSIFTW
Seems to do most of what yours does, but not limited to Windows.
I couldn't make it work with IE8, Firefox 3.6.9 and Seamonkey 2.0.2 on Windows :-(
With Firefox and Seamonkey it is stuck with the dialog "Parsing, standby...". If I close it, I get the editable text, and it seem to be complete, but I can't move the cursor or edit anything.
Cheers, Marc