--- a/testing/marionette/driver.js
+++ b/testing/marionette/driver.js
@@ -655,17 +655,17 @@ GeckoDriver.prototype.listeningPromise =
         resolve();
       }
     };
     this.mm.addMessageListener(li, cb);
   });
 };
 
 /** Create a new session. */
-GeckoDriver.prototype.newSession = function* (cmd, resp) {
+GeckoDriver.prototype.newSession = async function(cmd, resp) {
   if (this.sessionID) {
     throw new SessionNotCreatedError("Maximum number of active sessions");
   }
 
   this.sessionID = cmd.parameters.sessionId || element.generateUUID();
   this.newSessionCommandId = cmd.id;
 
   try {
@@ -733,18 +733,18 @@ GeckoDriver.prototype.newSession = funct
     this.addBrowser(win);
     this.whenBrowserStarted(win, false);
     this.mm.broadcastAsyncMessage("Marionette:restart", {});
   } else {
     throw new WebDriverError("Session already running");
   }
   this.switchToGlobalMessageManager();
 
-  yield registerBrowsers;
-  yield browserListening;
+  await registerBrowsers;
+  await browserListening;
 
   if (this.curBrowser.tab) {
     this.curBrowser.contentBrowser.focus();
   }
 
   // Setup global listener for modal dialogs, and check if there is already
   // one open for the currently selected browser window.
   modal.addHandler(this.dialogHandler);