--- a/toolkit/components/search/tests/xpcshell/head_search.js
+++ b/toolkit/components/search/tests/xpcshell/head_search.js
@@ -343,17 +343,21 @@ var gDataUrl;
  *
  * @return The HttpServer object in case further customization is needed.
  */
 function useHttpServer() {
   let httpServer = new HttpServer();
   httpServer.start(-1);
   httpServer.registerDirectory("/", do_get_cwd());
   gDataUrl = "http://localhost:" + httpServer.identity.primaryPort + "/data/";
-  do_register_cleanup(() => httpServer.stop(() => {}));
+  do_register_cleanup(function* cleanup_httpServer() {
+    yield new Promise(resolve => {
+      httpServer.stop(resolve);
+    });
+  });
   return httpServer;
 }
 
 /**
  * Adds test engines and returns a promise resolved when they are installed.
  *
  * The engines are added in the given order.
  *