diff --git a/addon-sdk/source/lib/sdk/loader/cuddlefish.js b/addon-sdk/source/lib/sdk/loader/cuddlefish.js
index aec0cea470d..f6b8b45cb15 100644
--- a/addon-sdk/source/lib/sdk/loader/cuddlefish.js
+++ b/addon-sdk/source/lib/sdk/loader/cuddlefish.js
@@ -14,25 +14,74 @@ module.metadata = {
 require('chrome')                  // Otherwise CFX will complain about Components
 require('toolkit/loader')          // Otherwise CFX will stip out loader.js
 require('sdk/addon/runner')        // Otherwise CFX will stip out addon/runner.js
+require('sdk/system/xul-app')      // Otherwise CFX will stip out sdk/system/xul-app
 */
 
 const { classes: Cc, Constructor: CC, interfaces: Ci, utils: Cu } = Components;
 
-const {
-  incompatibility
-} = Cu.import("resource://gre/modules/sdk/system/XulApp.js", {}).XulApp;
-
 // `loadSandbox` is exposed by bootstrap.js
 const loaderURI = module.uri.replace("sdk/loader/cuddlefish.js",
                                      "toolkit/loader.js");
+const xulappURI = module.uri.replace("loader/cuddlefish.js",
+                                     "system/xul-app.js");
 // We need to keep a reference to the sandbox in order to unload it in
 // bootstrap.js
 
 const loaderSandbox = loadSandbox(loaderURI);
 const loaderModule = loaderSandbox.exports;
 
+const xulappSandbox = loadSandbox(xulappURI);
+const xulappModule = xulappSandbox.exports;
+
 const { override, load } = loaderModule;
 
+/**
+ * Ensure the current application satisfied the requirements specified in the
+ * module given. If not, an exception related to the incompatibility is
+ * returned; `null` otherwise.
+ *
+ * @param {Object} module
+ *  The module to check
+ * @returns {Error}
+ */
+function incompatibility(module) {
+  let { metadata, id } = module;
+
+  // if metadata or engines are not specified we assume compatibility is not
+  // an issue.
+  if (!metadata || !("engines" in metadata))
+    return null;
+
+  let { engines } = metadata;
+
+  if (engines === null || typeof(engines) !== "object")
+    return new Error("Malformed engines' property in metadata");
+
+  let applications = Object.keys(engines);
+
+  let versionRange;
+  applications.forEach(function(name) {
+    if (xulappModule.is(name)) {
+      versionRange = engines[name];
+      // Continue iteration. We want to ensure the module doesn't
+      // contain a typo in the applications' name or some unknown
+      // application - `is` function throws an exception in that case.
+    }
+  });
+
+  if (typeof(versionRange) === "string") {
+    if (xulappModule.satisfiesVersion(versionRange))
+      return null;
+
+    return new Error("Unsupported Application version: The module " + id +
+            " currently supports only version " + versionRange + " of " +
+            xulappModule.name + ".");
+  }
+
+  return new Error("Unsupported Application: The module " + id +
+            " currently supports only " + applications.join(", ") + ".")
+}
+
 function CuddlefishLoader(options) {
   let { manifest } = options;
 
@@ -41,7 +90,8 @@ function CuddlefishLoader(options) {
     // cache to avoid subsequent loads via `require`.
     modules: override({
       'toolkit/loader': loaderModule,
-      'sdk/loader/cuddlefish': exports
+      'sdk/loader/cuddlefish': exports,
+      'sdk/system/xul-app': xulappModule
     }, options.modules),
     resolve: function resolve(id, requirer) {
       let entry = requirer && requirer in manifest && manifest[requirer];
diff --git a/addon-sdk/source/lib/toolkit/loader.js b/addon-sdk/source/lib/toolkit/loader.js
index e3add6ab79c..d2b17a1ab03 100644
--- a/addon-sdk/source/lib/toolkit/loader.js
+++ b/addon-sdk/source/lib/toolkit/loader.js
@@ -42,9 +42,6 @@ const { NetUtil } = Cu.import("resource://gre/modules/NetUtil.jsm", {});
 const { Reflect } = Cu.import("resource://gre/modules/reflect.jsm", {});
 const { ConsoleAPI } = Cu.import("resource://gre/modules/devtools/Console.jsm");
 const { join: pathJoin, normalize, dirname } = Cu.import("resource://gre/modules/osfile/ospath_unix.jsm");
-const {
-  incompatibility
-} = Cu.import("resource://gre/modules/sdk/system/XulApp.js", {}).XulApp;
 
 // Define some shortcuts.
 const bind = Function.call.bind(Function.bind);
@@ -352,12 +349,6 @@ const load = iced(function load(loader, module) {
     });
   }
 
-  let (error = incompatibility(module)) {
-    if (error) {
-      throw error;
-    }
-  }
-
   if (module.exports && typeof(module.exports) === 'object')
     freeze(module.exports);
 
diff --git a/addon-sdk/source/modules/system/XulApp.js b/addon-sdk/source/modules/system/XulApp.js
index db3b0f7e7df..68148be3a80 100644
--- a/addon-sdk/source/modules/system/XulApp.js
+++ b/addon-sdk/source/modules/system/XulApp.js
@@ -183,51 +183,3 @@ function satisfiesVersion(version, versionRange) {
   });
 }
 exports.satisfiesVersion = satisfiesVersion;
-
-/**
- * Ensure the current application satisfied the requirements specified in the
- * module given. If not, an exception related to the incompatibility is
- * returned; `null` otherwise.
- *
- * @param {Object} module
- *  The module to check
- * @returns {Error}
- */
-function incompatibility(module) {
-  let { metadata, id } = module;
-
-  // if metadata or engines are not specified we assume compatibility is not
-  // an issue.
-  if (!metadata || !("engines" in metadata))
-    return null;
-
-  let { engines } = metadata;
-
-  if (engines === null || typeof(engines) !== "object")
-    return new Error("Malformed engines' property in metadata");
-
-  let applications = Object.keys(engines);
-
-  let versionRange;
-  applications.forEach(function(name) {
-    if (is(name)) {
-      versionRange = engines[name];
-      // Continue iteration. We want to ensure the module doesn't
-      // contain a typo in the applications' name or some unknown
-      // application - `is` function throws an exception in that case.
-    }
-  });
-
-  if (typeof(versionRange) === "string") {
-    if (satisfiesVersion(versionRange))
-      return null;
-
-    return new Error("Unsupported Application version: The module " + id +
-            " currently supports only version " + versionRange + " of " +
-            name + ".");
-  }
-
-  return new Error("Unsupported Application: The module " + id +
-            " currently supports only " + applications.join(", ") + ".")
-}
-exports.incompatibility = incompatibility;
diff --git a/addon-sdk/source/test/test-cuddlefish.js b/addon-sdk/source/test/test-cuddlefish.js
index f28abc0a189..2d8bb6102a3 100644
--- a/addon-sdk/source/test/test-cuddlefish.js
+++ b/addon-sdk/source/test/test-cuddlefish.js
@@ -1,10 +1,10 @@
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
 'use strict';
 
 const { Loader, Require, unload, override } = require('sdk/loader/cuddlefish');
-const app = require('sdk/system/xul-app');
 const packaging = require('@loader/options');
 
 exports['test loader'] = function(assert) {
@@ -44,19 +44,4 @@ exports['test loader'] = function(assert) {
                'loader.unload() must call listeners in LIFO order.');
 };
 
-exports['test loader on unsupported modules'] = function(assert) {
-  let loader = Loader({});
-  let err = "";
-  assert.throws(() => {
-    if (!app.is('Firefox')) {
-      require('./fixtures/loader/unsupported/firefox');
-    }
-    else {
-      require('./fixtures/loader/unsupported/fennec');
-    }
-  }, /^Unsupported Application/, "throws Unsupported Application");
-
-  unload(loader);
-};
-
-require('sdk/test').run(exports);
+require('test').run(exports);
diff --git a/addon-sdk/source/test/test-loader.js b/addon-sdk/source/test/test-loader.js
index d948c3596fb..03ea1b3e0a1 100644
--- a/addon-sdk/source/test/test-loader.js
+++ b/addon-sdk/source/test/test-loader.js
@@ -1,6 +1,7 @@
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
 'use strict';
 
 let {
@@ -10,10 +11,9 @@ let { readURI } = require('sdk/net/url');
 
 let root = module.uri.substr(0, module.uri.lastIndexOf('/'))
 
+
 // The following adds Debugger constructor to the global namespace.
 const { Cu } = require('chrome');
-const app = require('sdk/system/xul-app');
-
 const { addDebuggerToGlobal } = Cu.import('resource://gre/modules/jsdebugger.jsm', {});
 addDebuggerToGlobal(this);
 
@@ -331,7 +331,7 @@ exports['test console global by default'] = function (assert) {
   let uri = root + '/fixtures/loader/globals/';
   let loader = Loader({ paths: { '': uri }});
   let program = main(loader, 'main');
-
+ 
   assert.ok(typeof program.console === 'object', 'global `console` exists');
   assert.ok(typeof program.console.log === 'function', 'global `console.log` exists');
 
@@ -366,19 +366,4 @@ exports['test shared globals'] = function(assert) {
   unload(loader);
 }
 
-exports['test loader on unsupported modules'] = function(assert) {
-  let loader = Loader({});
-  let err = "";
-  assert.throws(() => {
-    if (!app.is('Firefox')) {
-      require('./fixtures/loader/unsupported/firefox');
-    }
-    else {
-      require('./fixtures/loader/unsupported/fennec');
-    }
-  }, /^Unsupported Application/, "throws Unsupported Application");
-
-  unload(loader);
-};
-
-require('sdk/test').run(exports);
+require('test').run(exports);