Bug 680431, test_bug511075.html is calling finish() twice, f-smaug

layout/xul/base/test/test_bug511075.html

@@ -68,6 +68,7 @@ var tests = [
     synthesizeMouse(scroller, x, y, { type: "mouseup" }, window);
   },
   function() {
+    scroller.onscroll = null;
     ok(true, "Clicking the scrollbar should scroll");
     finish();
   }