--- a/js/xpconnect/loader/XPCOMUtils.jsm
+++ b/js/xpconnect/loader/XPCOMUtils.jsm
@@ -90,16 +90,18 @@
 
 this.EXPORTED_SYMBOLS = [ "XPCOMUtils" ];
 
 const Cc = Components.classes;
 const Ci = Components.interfaces;
 const Cr = Components.results;
 const Cu = Components.utils;
 
+const modules = {};
+
 this.XPCOMUtils = {
   /**
    * Generate a QueryInterface implementation. The returned function must be
    * assigned to the 'QueryInterface' property of a JS object. When invoked on
    * that object, it checks if the given iid is listed in the |interfaces|
    * param, and if it is, returns |this| (the object it was called on).
    * If the JS object has a classInfo property it'll be returned for the
    * nsIClassInfo IID, generateCI can be used to generate the classInfo
@@ -298,30 +300,43 @@ this.XPCOMUtils = {
                                    aPreLambda, aPostLambda, aProxy)
   {
     let proxy = aProxy || {};
 
     if (typeof(aPreLambda) === "function") {
       aPreLambda.apply(proxy);
     }
 
-    this.defineLazyGetter(aObject, aName, function XPCU_moduleLambda() {
-      var temp = {};
+    function XPCU_moduleLambda() {
       try {
-        Cu.import(aResource, temp);
+        let temp;
+        if (aResource in modules) {
+          temp = modules[aResource];
+        } else {
+          temp = {};
+          Cu.import(aResource, temp);
+          modules[aResource] = temp;
+        }
 
         if (typeof(aPostLambda) === "function") {
           aPostLambda.apply(proxy);
         }
+
+        return temp[aSymbol || aName];
       } catch (ex) {
         Cu.reportError("Failed to load module " + aResource + ".");
         throw ex;
       }
-      return temp[aSymbol || aName];
-    });
+    }
+
+    if (!aPostLambda && (aResource in modules || Cu.isModuleLoaded(aResource))) {
+      aObject[aSymbol || aName] = XPCU_moduleLambda();
+    } else {
+      this.defineLazyGetter(aObject, aName, XPCU_moduleLambda);
+    }
   },
 
   /**
    * Defines a getter on a specified object for preference value. The
    * preference is read the first time that the property is accessed,
    * and is thereafter kept up-to-date using a preference observer.
    *
    * @param aObject