--- a/toolkit/components/extensions/ext-notifications.js
+++ b/toolkit/components/extensions/ext-notifications.js
@@ -49,20 +49,20 @@ Notification.prototype = {
       // This will fail if the OS doesn't support this function.
     }
     notificationsMap.get(this.extension).delete(this.id);
   },
 
   observe(subject, topic, data) {
     let notifications = notificationsMap.get(this.extension);
 
-    function emitAndDelete(event) {
+    let emitAndDelete = event => {
       notifications.emit(event, data);
       notifications.delete(this.id);
-    }
+    };
 
     // Don't try to emit events if the extension has been unloaded
     if (!notifications) {
       return;
     }
 
     if (topic === "alertclickcallback") {
       emitAndDelete("clicked");