plugin must be called an 'extension' rather than an 'item' for FF to recognize the update.rdf

direct/src/plugin_installer/make_installer.py

@@ -130,7 +130,7 @@ update_rdf = """<?xml version="1.0"?>
 <RDF:RDF xmlns:RDF="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
          xmlns:em="http://www.mozilla.org/2004/em-rdf#">
 
-  <RDF:Description about="urn:mozilla:item:%(package_id)s">
+  <RDF:Description about="urn:mozilla:extension:%(package_id)s">
     <em:updates>
       <RDF:Seq>
         <RDF:li>