The Tor Browser / file revision

 var file;

 addMessageListener("file.create", function (message) {

   file = Components.classes["@mozilla.org/file/directory_service;1"]

              .getService(Components.interfaces.nsIProperties)

              .get("TmpD", Components.interfaces.nsIFile);

   file.append("foo.txt");

   file.createUnique(Components.interfaces.nsIFile.NORMAL_FILE_TYPE, 0600);

   sendAsyncMessage("file.path", file.path);

 });

 addMessageListener("file.remove", function (message) {

   file.remove(false);

   sendAsyncMessage("file.removed", {});

 });