<object type="application/x-ms-wmp" width="300" height="300">
<param name="URL" value="file.mp3">
One possible solution: When loading np-mswmp.dll (or whatever it might be named as), check the description and supported mime types to see that you really have the Firefox WMP plugin. If so, set a js_not_required flag or something. That way, you can still require JS for the old plugin and not require JS for the new one.
NPAPI plugin and Webkit plugins ae not supported anymore. Can this be marked as "RESOLVED WONTFIX"? Thanks!