new file mode 100644
--- /dev/null
+++ b/dom/base/ScriptableContentIterator.cpp
@@ -0,0 +1,145 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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/. */
+
+#include "ScriptableContentIterator.h"
+#include "nsINode.h"
+#include "nsRange.h"
+
+namespace mozilla {
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(ScriptableContentIterator)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(ScriptableContentIterator)
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(ScriptableContentIterator)
+  NS_INTERFACE_MAP_ENTRY(nsIScriptableContentIterator)
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
+NS_INTERFACE_MAP_END
+
+NS_IMPL_CYCLE_COLLECTION(ScriptableContentIterator, mContentIterator)
+
+ScriptableContentIterator::ScriptableContentIterator()
+    : mIteratorType(NOT_INITIALIZED) {}
+
+void ScriptableContentIterator::EnsureContentIterator() {
+  if (mContentIterator) {
+    return;
+  }
+  switch (mIteratorType) {
+    case POST_ORDER_ITERATOR:
+    default:
+      mContentIterator = NS_NewContentIterator();
+      break;
+    case PRE_ORDER_ITERATOR:
+      mContentIterator = NS_NewPreContentIterator();
+      break;
+    case SUBTREE_ITERATOR:
+      mContentIterator = NS_NewContentSubtreeIterator();
+      break;
+  }
+}
+
+NS_IMETHODIMP
+ScriptableContentIterator::InitWithRootNode(IteratorType aType,
+                                            nsINode* aRoot) {
+  if (aType == NOT_INITIALIZED ||
+      (mIteratorType != NOT_INITIALIZED && aType != mIteratorType)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+  mIteratorType = aType;
+  EnsureContentIterator();
+  return mContentIterator->Init(aRoot);
+}
+
+NS_IMETHODIMP
+ScriptableContentIterator::InitWithRange(IteratorType aType, nsRange* aRange) {
+  if (aType == NOT_INITIALIZED ||
+      (mIteratorType != NOT_INITIALIZED && aType != mIteratorType)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+  mIteratorType = aType;
+  EnsureContentIterator();
+  return mContentIterator->Init(aRange);
+}
+
+NS_IMETHODIMP
+ScriptableContentIterator::InitWithPositions(IteratorType aType,
+                                             nsINode* aStartContainer,
+                                             uint32_t aStartOffset,
+                                             nsINode* aEndContainer,
+                                             uint32_t aEndOffset) {
+  if (aType == NOT_INITIALIZED ||
+      (mIteratorType != NOT_INITIALIZED && aType != mIteratorType)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+  mIteratorType = aType;
+  EnsureContentIterator();
+  return mContentIterator->Init(aStartContainer, aStartOffset, aEndContainer,
+                                aEndOffset);
+}
+
+NS_IMETHODIMP
+ScriptableContentIterator::First() {
+  if (!mContentIterator) {
+    return NS_ERROR_NOT_INITIALIZED;
+  }
+  mContentIterator->First();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+ScriptableContentIterator::Last() {
+  if (!mContentIterator) {
+    return NS_ERROR_NOT_INITIALIZED;
+  }
+  mContentIterator->Last();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+ScriptableContentIterator::Next() {
+  if (!mContentIterator) {
+    return NS_ERROR_NOT_INITIALIZED;
+  }
+  mContentIterator->Next();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+ScriptableContentIterator::Prev() {
+  if (!mContentIterator) {
+    return NS_ERROR_NOT_INITIALIZED;
+  }
+  mContentIterator->Prev();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+ScriptableContentIterator::GetCurrentNode(nsINode** aNode) {
+  if (!mContentIterator) {
+    return NS_ERROR_NOT_INITIALIZED;
+  }
+  NS_IF_ADDREF(*aNode = mContentIterator->GetCurrentNode());
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+ScriptableContentIterator::GetIsDone(bool* aIsDone) {
+  if (!mContentIterator) {
+    return NS_ERROR_NOT_INITIALIZED;
+  }
+  *aIsDone = mContentIterator->IsDone();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+ScriptableContentIterator::PositionAt(nsINode* aNode) {
+  if (!mContentIterator) {
+    return NS_ERROR_NOT_INITIALIZED;
+  }
+  return mContentIterator->PositionAt(aNode);
+}
+
+}  // namespace mozilla

new file mode 100644
--- /dev/null
+++ b/dom/base/ScriptableContentIterator.h
@@ -0,0 +1,34 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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/. */
+
+#ifndef mozilla_scriptablecontentiterator_h
+#define mozilla_scriptablecontentiterator_h
+
+#include "mozilla/Attributes.h"
+#include "nsCOMPtr.h"
+#include "nsIContentIterator.h"
+#include "nsIScriptableContentIterator.h"
+
+namespace mozilla {
+
+class ScriptableContentIterator final : public nsIScriptableContentIterator {
+ public:
+  ScriptableContentIterator();
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+  NS_DECL_CYCLE_COLLECTION_CLASS(ScriptableContentIterator)
+  NS_DECL_NSISCRIPTABLECONTENTITERATOR
+
+ protected:
+  virtual ~ScriptableContentIterator() = default;
+  void EnsureContentIterator();
+
+  IteratorType mIteratorType;
+  nsCOMPtr<nsIContentIterator> mContentIterator;
+};
+
+}  // namespace mozilla
+
+#endif  // #ifndef mozilla_scriptablecontentiterator_h

--- a/dom/base/moz.build
+++ b/dom/base/moz.build
@@ -18,16 +18,17 @@ XPIDL_SOURCES += [
     'nsIDocumentEncoder.idl',
     'nsIDOMRequestService.idl',
     'nsIDroppedLinkHandler.idl',
     'nsIFrameLoaderOwner.idl',
     'nsIImageLoadingContent.idl',
     'nsIMessageManager.idl',
     'nsIObjectLoadingContent.idl',
     'nsIRemoteWindowContext.idl',
+    'nsIScriptableContentIterator.idl',
     'nsIScriptChannel.idl',
     'nsISelectionController.idl',
     'nsISelectionDisplay.idl',
     'nsISelectionListener.idl',
     'nsISlowScriptDebug.idl',
 ]
 
 XPIDL_MODULE = 'dom'
@@ -124,16 +125,17 @@ if CONFIG['MOZ_WEBRTC']:
         'nsDOMDataChannelDeclarations.h',
     ]
 
 EXPORTS.mozilla += [
     'CORSMode.h',
     'FlushType.h',
     'FullscreenChange.h',
     'RangeBoundary.h',
+    'ScriptableContentIterator.h',
     'SelectionChangeEventDispatcher.h',
     'TextInputProcessor.h',
     'UseCounter.h',
 ]
 
 EXPORTS.mozilla.dom += [
     '!UseCounterList.h',
     'AnonymousContent.h',
@@ -370,16 +372,17 @@ UNIFIED_SOURCES += [
     'Pose.cpp',
     'PostMessageEvent.cpp',
     'ProcessMessageManager.cpp',
     'RemoteOuterWindowProxy.cpp',
     'ResponsiveImageSelector.cpp',
     'SameProcessMessageQueue.cpp',
     'ScreenLuminance.cpp',
     'ScreenOrientation.cpp',
+    'ScriptableContentIterator.cpp',
     'Selection.cpp',
     'SelectionChangeEventDispatcher.cpp',
     'ShadowRoot.cpp',
     'StorageAccessPermissionRequest.cpp',
     'StructuredCloneBlob.cpp',
     'StructuredCloneHolder.cpp',
     'StructuredCloneTester.cpp',
     'StyleSheetList.cpp',

new file mode 100644
--- /dev/null
+++ b/dom/base/nsIScriptableContentIterator.idl
@@ -0,0 +1,74 @@
+/* -*- Mode: IDL; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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/. */
+
+#include "nsISupports.idl"
+
+webidl Node;
+webidl Range;
+
+/**
+ * nsIScriptableContentIterator is designed to testing concrete classes of
+ * nsIContentIterator.
+ */
+[scriptable, builtinclass, uuid(9f25fb2a-265f-44f9-a122-62bbf443239e)]
+interface nsIScriptableContentIterator : nsISupports
+{
+  cenum IteratorType : 8 {
+    NOT_INITIALIZED,
+    POST_ORDER_ITERATOR,
+    PRE_ORDER_ITERATOR,
+    SUBTREE_ITERATOR
+  };
+
+  /**
+   * You need to call initWith*() first.  Then, the instance of this interface
+   * decides the type of iterator with its aType argument.  You can call
+   * initWith*() multiple times, but you need to keep setting same type as
+   * previous call.  If you set different type, these method with throw an
+   * exception.
+   */
+
+  // See nsIContentIterator::Init(nsINode*)
+  void initWithRootNode(in nsIScriptableContentIterator_IteratorType aType,
+                        in Node aRoot);
+
+  // See nsIContentIterator::Init(nsRange*)
+  void initWithRange(in nsIScriptableContentIterator_IteratorType aType,
+                     in Range aRange);
+
+  // See nsIContentIterator::Init(nsINode*, uint32_t, nsINode*, uint32_t)
+  void initWithPositions(in nsIScriptableContentIterator_IteratorType aType,
+                         in Node aStartContainer, in unsigned long aStartOffset,
+                         in Node aEndContainer, in unsigned long aEndOffset);
+
+  // See nsIContentIterator::First()
+  void first();
+
+  // See nsIContentIterator::Last()
+  void last();
+
+  // See nsIContentIterator::Next()
+  void next();
+
+  // See nsIContentIterator::Prev()
+  void prev();
+
+  // See nsIContentIterator::GetCurrentNode()
+  readonly attribute Node currentNode;
+
+  // See nsIContentIterator::IsDone()
+  readonly attribute bool isDone;
+
+  // See nsIContentIterator::PositionAt(nsINode*)
+  void positionAt(in Node aNode);
+};
+
+%{C++
+#define SCRIPTABLE_CONTENT_ITERATOR_CID \
+  { 0xf68037ec, 0x2790, 0x44c5, \
+    { 0x8e, 0x5f, 0xdf, 0x5d, 0xa5, 0x8b, 0x93, 0xa7 } }
+#define SCRIPTABLE_CONTENT_ITERATOR_CONTRACTID \
+  "@mozilla.org/scriptable-content-iterator;1"
+%}

--- a/layout/build/nsLayoutModule.cpp
+++ b/layout/build/nsLayoutModule.cpp
@@ -143,16 +143,17 @@ static void Shutdown();
 #include "mozilla/dom/PresentationDeviceManager.h"
 #include "mozilla/dom/PresentationTCPSessionTransport.h"
 
 #include "nsScriptError.h"
 #include "nsBaseCommandController.h"
 #include "nsControllerCommandTable.h"
 
 #include "mozilla/TextInputProcessor.h"
+#include "mozilla/ScriptableContentIterator.h"
 
 using namespace mozilla;
 using namespace mozilla::dom;
 using namespace mozilla::net;
 using mozilla::dom::power::PowerManagerService;
 using mozilla::dom::quota::QuotaManagerService;
 using mozilla::gmp::GeckoMediaPluginService;
 
@@ -215,16 +216,17 @@ NS_GENERIC_FACTORY_SINGLETON_CONSTRUCTOR
                                          MediaManager::GetInstance)
 NS_GENERIC_FACTORY_CONSTRUCTOR(PresentationDeviceManager)
 NS_GENERIC_FACTORY_CONSTRUCTOR(TextInputProcessor)
 NS_GENERIC_FACTORY_SINGLETON_CONSTRUCTOR(nsIPresentationService,
                                          NS_CreatePresentationService)
 NS_GENERIC_FACTORY_CONSTRUCTOR(PresentationTCPSessionTransport)
 NS_GENERIC_FACTORY_CONSTRUCTOR_INIT(NotificationTelemetryService, Init)
 NS_GENERIC_FACTORY_CONSTRUCTOR(PushNotifier)
+NS_GENERIC_FACTORY_CONSTRUCTOR(ScriptableContentIterator)
 
 //-----------------------------------------------------------------------------
 
 static bool gInitialized = false;
 
 // Perform our one-time intialization for this module
 
 void nsLayoutModuleInitialize() {
@@ -514,16 +516,18 @@ NS_DEFINE_NAMED_CID(GECKO_MEDIA_PLUGIN_S
 NS_DEFINE_NAMED_CID(PRESENTATION_SERVICE_CID);
 NS_DEFINE_NAMED_CID(PRESENTATION_DEVICE_MANAGER_CID);
 NS_DEFINE_NAMED_CID(PRESENTATION_TCP_SESSION_TRANSPORT_CID);
 
 NS_DEFINE_NAMED_CID(TEXT_INPUT_PROCESSOR_CID);
 
 NS_DEFINE_NAMED_CID(NS_SCRIPTERROR_CID);
 
+NS_DEFINE_NAMED_CID(SCRIPTABLE_CONTENT_ITERATOR_CID);
+
 static nsresult LocalStorageManagerConstructor(nsISupports* aOuter,
                                                REFNSIID aIID, void** aResult) {
   if (NextGenLocalStorageEnabled()) {
     RefPtr<LocalStorageManager2> manager = new LocalStorageManager2();
     return manager->QueryInterface(aIID, aResult);
   }
 
   RefPtr<LocalStorageManager> manager = new LocalStorageManager();
@@ -599,16 +603,17 @@ static const mozilla::Module::CIDEntry k
 #ifdef ACCESSIBILITY
   { &kNS_ACCESSIBILITY_SERVICE_CID, false, nullptr, CreateA11yService },
 #endif
   { &kPRESENTATION_SERVICE_CID, false, nullptr, nsIPresentationServiceConstructor },
   { &kPRESENTATION_DEVICE_MANAGER_CID, false, nullptr, PresentationDeviceManagerConstructor },
   { &kPRESENTATION_TCP_SESSION_TRANSPORT_CID, false, nullptr, PresentationTCPSessionTransportConstructor },
   { &kTEXT_INPUT_PROCESSOR_CID, false, nullptr, TextInputProcessorConstructor },
   { &kNS_SCRIPTERROR_CID, false, nullptr, nsScriptErrorConstructor },
+  { &kSCRIPTABLE_CONTENT_ITERATOR_CID, false, nullptr, ScriptableContentIteratorConstructor },
   { nullptr }
     // clang-format on
 };
 
 static const mozilla::Module::ContractIDEntry kLayoutContracts[] = {
     // clang-format off
   XPCONNECT_CONTRACTS
   { "@mozilla.org/inspector/deep-tree-walker;1", &kIN_DEEPTREEWALKER_CID },
@@ -671,16 +676,17 @@ static const mozilla::Module::ContractID
   { "@mozilla.org/accessibilityService;1", &kNS_ACCESSIBILITY_SERVICE_CID },
 #endif
   { "@mozilla.org/gecko-media-plugin-service;1",  &kGECKO_MEDIA_PLUGIN_SERVICE_CID },
   { PRESENTATION_SERVICE_CONTRACTID, &kPRESENTATION_SERVICE_CID },
   { PRESENTATION_DEVICE_MANAGER_CONTRACTID, &kPRESENTATION_DEVICE_MANAGER_CID },
   { PRESENTATION_TCP_SESSION_TRANSPORT_CONTRACTID, &kPRESENTATION_TCP_SESSION_TRANSPORT_CID },
   { "@mozilla.org/text-input-processor;1", &kTEXT_INPUT_PROCESSOR_CID },
   { NS_SCRIPTERROR_CONTRACTID, &kNS_SCRIPTERROR_CID },
+  { "@mozilla.org/scriptable-content-iterator;1", &kSCRIPTABLE_CONTENT_ITERATOR_CID },
   { nullptr }
 };
 
 static const mozilla::Module::CategoryEntry kLayoutCategories[] = {
   { "content-policy", NS_DATADOCUMENTCONTENTPOLICY_CONTRACTID, NS_DATADOCUMENTCONTENTPOLICY_CONTRACTID },
   { "content-policy", NS_NODATAPROTOCOLCONTENTPOLICY_CONTRACTID, NS_NODATAPROTOCOLCONTENTPOLICY_CONTRACTID },
   { "content-policy", "CSPService", CSPSERVICE_CONTRACTID },
   { "content-policy", NS_MIXEDCONTENTBLOCKER_CONTRACTID, NS_MIXEDCONTENTBLOCKER_CONTRACTID },