--- a/toolkit/components/extensions/Extension.jsm
+++ b/toolkit/components/extensions/Extension.jsm
@@ -1635,19 +1635,19 @@ class Extension extends ExtensionData {
         promises.push(Management.asyncEmitManifestEntry(this, directive));
       }
     }
 
     activeExtensionIDs.add(this.id);
     sharedData.set("extensions/activeIDs", activeExtensionIDs);
 
     Services.ppmm.sharedData.flush();
-    return this.broadcast("Extension:Startup", this.id).then(() => {
-      return Promise.all(promises);
-    });
+    this.broadcast("Extension:Startup", this.id);
+
+    return Promise.all(promises);
   }
 
   /**
    * Call the close() method on the given object when this extension
    * is shut down.  This can happen during browser shutdown, or when
    * an extension is manually disabled or uninstalled.
    *
    * @param {object} obj