diff --git a/js/xpconnect/idl/xpcIJSModuleLoader.idl b/js/xpconnect/idl/xpcIJSModuleLoader.idl
index 761f2809b44c..5f66b105a188 100644
--- a/js/xpconnect/idl/xpcIJSModuleLoader.idl
+++ b/js/xpconnect/idl/xpcIJSModuleLoader.idl
@@ -15,7 +15,7 @@ class nsAXPCNativeCallContext;
 
 [ptr] native JSObjectPtr(JSObject);
 
-[scriptable, uuid(243d1a31-db9f-47a1-9922-55a1ad5515fb)]
+[scriptable, uuid(4f94b21f-2920-4bd9-8251-5fb60fb054b2)]
 interface xpcIJSModuleLoader : nsISupports
 {
   /**
@@ -67,4 +67,16 @@ interface xpcIJSModuleLoader : nsISupports
    * then this method will do nothing.
    */
   void unload(in AUTF8String aResourceURI);
+
+  /**
+   * Returns true if the js file located at 'registryLocation' location has
+   * been loaded previously via the import method above. Returns false
+   * otherwise.
+   *
+   * @param resourceURI A resource:// URI string representing the location of
+   *        the js file to be checked if it is already loaded or not.
+   * @returns boolean, true if the js file has been loaded via import. false
+   *          otherwise
+   */
+  boolean isModuleLoaded(in AUTF8String aResourceURI);
 };
diff --git a/js/xpconnect/idl/xpccomponents.idl b/js/xpconnect/idl/xpccomponents.idl
index 2ccf9a982d0a..2d8221598616 100644
--- a/js/xpconnect/idl/xpccomponents.idl
+++ b/js/xpconnect/idl/xpccomponents.idl
@@ -21,7 +21,7 @@ interface nsIStackFrame;
 * interface of Components.interfacesByID
 * (interesting stuff only reflected into JavaScript)
 */
-[scriptable, uuid(c99cffac-5aed-4267-ad2f-f4a4c9d4a081)]
+[scriptable, uuid(f235ef76-9919-478b-aa0f-282d994ddf76)]
 interface nsIXPCComponents_InterfacesByID : nsISupports
 {
 };
@@ -217,6 +217,18 @@ interface nsIXPCComponents_Utils : nsISupports
     [implicit_jscontext,optional_argc]
     jsval import(in AUTF8String aResourceURI, [optional] in jsval targetObj);
 
+    /**
+     * Returns true if the js file located at 'registryLocation' location has
+     * been loaded previously via the import method above. Returns false
+     * otherwise.
+     *
+     * @param resourceURI A resource:// URI string representing the location of
+     *        the js file to be checked if it is already loaded or not.
+     * @returns boolean, true if the js file has been loaded via import. false
+     *          otherwise
+     */
+    boolean isModuleLoaded(in AUTF8String aResourceURI);
+
     /*
      * Unloads the JS module at 'registryLocation'. Existing references to the
      * module will continue to work but any subsequent import of the module will
diff --git a/js/xpconnect/loader/mozJSComponentLoader.cpp b/js/xpconnect/loader/mozJSComponentLoader.cpp
index 183ee9a9e30a..9bfe1eab5174 100644
--- a/js/xpconnect/loader/mozJSComponentLoader.cpp
+++ b/js/xpconnect/loader/mozJSComponentLoader.cpp
@@ -1210,6 +1210,27 @@ mozJSComponentLoader::ImportInto(const nsACString &aLocation,
     return NS_OK;
 }
 
+/* boolean isModuleLoaded (in AUTF8String registryLocation); */
+NS_IMETHODIMP
+mozJSComponentLoader::IsModuleLoaded(const nsACString& aLocation,
+                                     bool *retval)
+{
+    MOZ_ASSERT(nsContentUtils::IsCallerChrome());
+
+    nsresult rv;
+    if (!mInitialized) {
+        rv = ReallyInit();
+        NS_ENSURE_SUCCESS(rv, rv);
+    }
+
+    ComponentLoaderInfo info(aLocation);
+    rv = info.EnsureKey();
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    *retval = !!mImports.Get(info.Key());
+    return NS_OK;
+}
+
 nsresult
 mozJSComponentLoader::ImportInto(const nsACString &aLocation,
                                  HandleObject targetObj,
diff --git a/js/xpconnect/src/XPCComponents.cpp b/js/xpconnect/src/XPCComponents.cpp
index 525aa73a7f93..9da28aaae75b 100644
--- a/js/xpconnect/src/XPCComponents.cpp
+++ b/js/xpconnect/src/XPCComponents.cpp
@@ -2724,6 +2724,18 @@ nsXPCComponents_Utils::Import(const nsACString& registryLocation,
     return moduleloader->Import(registryLocation, targetObj, cx, optionalArgc, retval);
 }
 
+/* boolean isModuleLoaded (in AUTF8String registryLocation);
+ */
+NS_IMETHODIMP
+nsXPCComponents_Utils::IsModuleLoaded(const nsACString& registryLocation, bool *retval)
+{
+    nsCOMPtr<xpcIJSModuleLoader> moduleloader =
+        do_GetService(MOZJSCOMPONENTLOADER_CONTRACTID);
+    if (!moduleloader)
+        return NS_ERROR_FAILURE;
+    return moduleloader->IsModuleLoaded(registryLocation, retval);
+}
+
 /* unload (in AUTF8String registryLocation);
  */
 NS_IMETHODIMP
diff --git a/js/xpconnect/tests/unit/test_isModuleLoaded.js b/js/xpconnect/tests/unit/test_isModuleLoaded.js
new file mode 100644
index 000000000000..f08bf2def525
--- /dev/null
+++ b/js/xpconnect/tests/unit/test_isModuleLoaded.js
@@ -0,0 +1,33 @@
+const Cu = Components.utils;
+
+function run_test() {
+  // Existing module.
+  do_check_true(!Cu.isModuleLoaded("resource://gre/modules/devtools/LayoutHelpers.jsm"),
+                "isModuleLoaded returned correct value for non-loaded module");
+  Cu.import("resource://gre/modules/devtools/LayoutHelpers.jsm");
+  do_check_true(Cu.isModuleLoaded("resource://gre/modules/devtools/LayoutHelpers.jsm"),
+                "isModuleLoaded returned true after loading that module");
+  Cu.unload("resource://gre/modules/devtools/LayoutHelpers.jsm");
+  do_check_true(!Cu.isModuleLoaded("resource://gre/modules/devtools/LayoutHelpers.jsm"),
+                "isModuleLoaded returned false after unloading that module");
+
+  // Non-existing module
+  do_check_true(!Cu.isModuleLoaded("resource://gre/modules/devtools/LayoutHelpers1.jsm"),
+                "isModuleLoaded returned correct value for non-loaded module");
+  try {
+    Cu.import("resource://gre/modules/devtools/LayoutHelpers1.jsm");
+    do_check_true(false,
+                  "Should have thrown while trying to load a non existing file");
+  } catch (ex) {}
+  do_check_true(!Cu.isModuleLoaded("resource://gre/modules/devtools/LayoutHelpers1.jsm"),
+                "isModuleLoaded returned correct value for non-loaded module");
+
+  // incorrect url
+  try {
+    Cu.isModuleLoaded("resource://modules/devtools/LayoutHelpers1.jsm");
+    do_check_true(false,
+                  "Should have thrown while trying to load a non existing file");
+  } catch (ex) {
+    do_check_true(true, "isModuleLoaded threw an exception while loading incorrect uri");
+  }
+}
diff --git a/js/xpconnect/tests/unit/xpcshell.ini b/js/xpconnect/tests/unit/xpcshell.ini
index f4b37d48a2ab..bfea4b1d0c5e 100644
--- a/js/xpconnect/tests/unit/xpcshell.ini
+++ b/js/xpconnect/tests/unit/xpcshell.ini
@@ -49,6 +49,7 @@ support-files =
 [test_file2.js]
 [test_import.js]
 [test_import_fail.js]
+[test_isModuleLoaded.js]
 [test_js_weak_references.js]
 [test_reflect_parse.js]
 [test_localeCompare.js]