--- a/toolkit/xre/nsXREDirProvider.cpp
+++ b/toolkit/xre/nsXREDirProvider.cpp
@@ -1096,16 +1096,24 @@ nsXREDirProvider::DoShutdown()
   if (mProfileNotified) {
     nsCOMPtr<nsIObserverService> obsSvc =
       mozilla::services::GetObserverService();
     NS_ASSERTION(obsSvc, "No observer service?");
     if (obsSvc) {
       static const char16_t kShutdownPersist[] = u"shutdown-persist";
       obsSvc->NotifyObservers(nullptr, "profile-change-net-teardown", kShutdownPersist);
       obsSvc->NotifyObservers(nullptr, "profile-change-teardown", kShutdownPersist);
+
+#ifdef DEBUG
+      // Not having this causes large intermittent leaks. See bug 1340425.
+      if (JSContext* cx = dom::danger::GetJSContext()) {
+        JS_GC(cx);
+      }
+#endif
+
       obsSvc->NotifyObservers(nullptr, "profile-before-change", kShutdownPersist);
       obsSvc->NotifyObservers(nullptr, "profile-before-change-qm", kShutdownPersist);
       obsSvc->NotifyObservers(nullptr, "profile-before-change-telemetry", kShutdownPersist);
     }
     mProfileNotified = false;
   }
 
 #if (defined(XP_WIN) || defined(XP_MACOSX)) && defined(MOZ_CONTENT_SANDBOX)