diff --git a/dom/apps/src/AppDownloadManager.jsm b/dom/apps/src/AppDownloadManager.jsm
index 0a4ec53617df..412d68f088e6 100644
--- a/dom/apps/src/AppDownloadManager.jsm
+++ b/dom/apps/src/AppDownloadManager.jsm
@@ -8,7 +8,10 @@ const Cc = Components.classes;
 const Ci = Components.interfaces;
 const Cu = Components.utils;
 
-Cu.import("resource://gre/modules/FreeSpaceWatcher.jsm");
+Cu.import("resource://gre/modules/XPCOMUtils.jsm");
+
+XPCOMUtils.defineLazyModuleGetter(this, "FreeSpaceWatcher",
+                                  "resource://gre/modules/FreeSpaceWatcher.jsm");
 
 this.EXPORTED_SYMBOLS = ["AppDownloadManager"];