--- a/layout/base/PresShell.cpp
+++ b/layout/base/PresShell.cpp
@@ -54,17 +54,16 @@
 #include "nsView.h"
 #include "nsCRTGlue.h"
 #include "prinrval.h"
 #include "nsTArray.h"
 #include "nsCOMArray.h"
 #include "nsContainerFrame.h"
 #include "mozilla/dom/Selection.h"
 #include "nsGkAtoms.h"
-#include "nsIDOMDocument.h"
 #include "nsIDOMNode.h"
 #include "nsRange.h"
 #include "nsWindowSizes.h"
 #include "nsCOMPtr.h"
 #include "nsAutoPtr.h"
 #include "nsReadableUtils.h"
 #include "nsIPageSequenceFrame.h"
 #include "nsIPermissionManager.h"

--- a/layout/base/nsDocumentViewer.cpp
+++ b/layout/base/nsDocumentViewer.cpp
@@ -23,17 +23,16 @@
 #include "nsPresContext.h"
 #include "nsIPresShell.h"
 #include "nsIFrame.h"
 #include "nsIWritablePropertyBag2.h"
 #include "nsSubDocumentFrame.h"
 #include "nsGenericHTMLElement.h"
 
 #include "nsILinkHandler.h"
-#include "nsIDOMDocument.h"
 #include "nsISelectionListener.h"
 #include "mozilla/dom/Selection.h"
 #include "nsContentUtils.h"
 #include "nsLayoutStylesheetCache.h"
 #ifdef ACCESSIBILITY
 #include "mozilla/a11y/DocAccessible.h"
 #endif
 #include "mozilla/BasicEvents.h"

--- a/layout/generic/nsFrameSelection.cpp
+++ b/layout/generic/nsFrameSelection.cpp
@@ -54,17 +54,16 @@ static NS_DEFINE_CID(kFrameTraversalCID,
 #include "nsCaret.h"
 #include "AccessibleCaretEventHub.h"
 
 #include "mozilla/MouseEvents.h"
 #include "mozilla/TextEvents.h"
 
 #include "nsITimer.h"
 // notifications
-#include "nsIDOMDocument.h"
 #include "nsIDocument.h"
 
 #include "nsISelectionController.h" //for the enums
 #include "nsAutoCopyListener.h"
 #include "SelectionChangeListener.h"
 #include "nsCopySupport.h"
 #include "nsIClipboard.h"
 #include "nsIFrameInlines.h"

--- a/layout/inspector/InspectorUtils.cpp
+++ b/layout/inspector/InspectorUtils.cpp
@@ -12,17 +12,16 @@
 #include "nsArray.h"
 #include "nsAutoPtr.h"
 #include "nsIServiceManager.h"
 #include "nsString.h"
 #include "nsIStyleSheetLinkingElement.h"
 #include "nsIContentInlines.h"
 #include "nsIDocument.h"
 #include "nsIPresShell.h"
-#include "nsIDOMDocument.h"
 #include "nsIDOMWindow.h"
 #include "nsXBLBinding.h"
 #include "nsXBLPrototypeBinding.h"
 #include "nsIMutableArray.h"
 #include "nsBindingManager.h"
 #include "ChildIterator.h"
 #include "nsComputedDOMStyle.h"
 #include "mozilla/EventStateManager.h"

--- a/layout/inspector/inDeepTreeWalker.cpp
+++ b/layout/inspector/inDeepTreeWalker.cpp
@@ -3,17 +3,17 @@
 /* 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 "inDeepTreeWalker.h"
 #include "inLayoutUtils.h"
 
 #include "nsString.h"
-#include "nsIDOMDocument.h"
+#include "nsIDocument.h"
 #include "nsServiceManagerUtils.h"
 #include "nsIContent.h"
 #include "ChildIterator.h"
 #include "mozilla/dom/Element.h"
 #include "mozilla/dom/InspectorUtils.h"
 #include "mozilla/dom/NodeFilterBinding.h"
 
 /*****************************************************************************
@@ -160,17 +160,18 @@ static already_AddRefed<nsINodeList>
 GetChildren(nsIDOMNode* aParent,
             bool aShowAnonymousContent,
             bool aShowSubDocuments)
 {
   MOZ_ASSERT(aParent);
 
   nsCOMPtr<nsINodeList> ret;
   if (aShowSubDocuments) {
-    nsCOMPtr<nsIDOMDocument> domdoc = inLayoutUtils::GetSubDocumentFor(aParent);
+    nsCOMPtr<nsIDOMNode> domdoc =
+      do_QueryInterface(inLayoutUtils::GetSubDocumentFor(aParent));
     if (domdoc) {
       aParent = domdoc;
     }
   }
 
   nsCOMPtr<nsIContent> parentAsContent = do_QueryInterface(aParent);
   if (parentAsContent && aShowAnonymousContent) {
       ret = parentAsContent->GetChildren(nsIContent::eAllChildren);
@@ -293,17 +294,18 @@ inDeepTreeWalker::EdgeChild(nsIDOMNode**
 
   *_retval = nullptr;
 
   nsCOMPtr<nsIDOMNode> echild;
   if (mShowSubDocuments && mShowDocumentsAsNodes) {
     // GetChildren below, will skip the document node from
     // the walk. But if mShowDocumentsAsNodes is set to true
     // we want to include the (sub)document itself too.
-    echild = inLayoutUtils::GetSubDocumentFor(mCurrentNode);
+    echild =
+      do_QueryInterface(inLayoutUtils::GetSubDocumentFor(mCurrentNode));
   }
 
   nsCOMPtr<nsINodeList> children;
   if (!echild) {
     children = GetChildren(mCurrentNode,
                            mShowAnonymousContent,
                            mShowSubDocuments);
     if (children && children->Length() > 0) {

--- a/layout/inspector/inLayoutUtils.cpp
+++ b/layout/inspector/inLayoutUtils.cpp
@@ -2,17 +2,16 @@
 /* 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 "inLayoutUtils.h"
 
 #include "nsIDocument.h"
-#include "nsIDOMDocument.h"
 #include "nsIContent.h"
 #include "nsIContentViewer.h"
 #include "nsPIDOMWindow.h"
 #include "nsIDocShell.h"
 #include "nsIPresShell.h"
 #include "nsPresContext.h"
 #include "mozilla/EventStateManager.h"
 #include "mozilla/dom/Element.h"
@@ -27,26 +26,24 @@ inLayoutUtils::GetEventStateManagerFor(E
   nsIDocument* doc = aElement.OwnerDoc();
   nsPresContext* presContext = doc->GetPresContext();
   if (!presContext)
     return nullptr;
 
   return presContext->EventStateManager();
 }
 
-nsIDOMDocument*
+nsIDocument*
 inLayoutUtils::GetSubDocumentFor(nsIDOMNode* aNode)
 {
   nsCOMPtr<nsIContent> content = do_QueryInterface(aNode);
   if (content) {
     nsCOMPtr<nsIDocument> doc = content->GetComposedDoc();
     if (doc) {
-      nsCOMPtr<nsIDOMDocument> domdoc(do_QueryInterface(doc->GetSubDocumentFor(content)));
-
-      return domdoc;
+      return doc->GetSubDocumentFor(content);
     }
   }
 
   return nullptr;
 }
 
 nsINode*
 inLayoutUtils::GetContainerFor(const nsIDocument& aDoc)

--- a/layout/inspector/inLayoutUtils.h
+++ b/layout/inspector/inLayoutUtils.h
@@ -3,29 +3,28 @@
 /* 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 __inLayoutUtils_h__
 #define __inLayoutUtils_h__
 
 class nsIDocument;
-class nsIDOMDocument;
 class nsIDOMNode;
 class nsINode;
 
 namespace mozilla {
 class EventStateManager;
 namespace dom {
 class Element;
 } // namespace dom
 } // namespace mozilla
 
 class inLayoutUtils
 {
 public:
   static mozilla::EventStateManager* GetEventStateManagerFor(
       mozilla::dom::Element& aElement);
-  static nsIDOMDocument* GetSubDocumentFor(nsIDOMNode* aNode);
+  static nsIDocument* GetSubDocumentFor(nsIDOMNode* aNode);
   static nsINode* GetContainerFor(const nsIDocument& aDoc);
 };
 
 #endif // __inLayoutUtils_h__

--- a/layout/printing/nsPrintJob.cpp
+++ b/layout/printing/nsPrintJob.cpp
@@ -71,17 +71,16 @@ static const char kPrintingPromptService
 #include "nsISelectionController.h"
 
 // Misc
 #include "gfxContext.h"
 #include "mozilla/gfx/DrawEventRecorder.h"
 #include "mozilla/layout/RemotePrintJobChild.h"
 #include "nsISupportsUtils.h"
 #include "nsIScriptContext.h"
-#include "nsIDOMDocument.h"
 #include "nsIDocumentObserver.h"
 #include "nsISelectionListener.h"
 #include "nsContentCID.h"
 #include "nsLayoutCID.h"
 #include "nsContentUtils.h"
 #include "nsIPresShell.h"
 #include "nsLayoutStylesheetCache.h"
 #include "nsLayoutUtils.h"
@@ -615,17 +614,17 @@ static void DumpLayoutData(const char* a
 #endif
 
 //--------------------------------------------------------------------------------
 
 nsresult
 nsPrintJob::CommonPrint(bool                    aIsPrintPreview,
                         nsIPrintSettings*       aPrintSettings,
                         nsIWebProgressListener* aWebProgressListener,
-                        nsIDOMDocument* aDoc)
+                        nsIDocument* aDoc)
 {
   // Callers must hold a strong reference to |this| to ensure that we stay
   // alive for the duration of this method, because our main owning reference
   // (on nsDocumentViewer) might be cleared during this function (if we cause
   // script to run and it cancels the print operation).
 
   nsresult rv = DoCommonPrint(aIsPrintPreview, aPrintSettings,
                               aWebProgressListener, aDoc);
@@ -646,17 +645,17 @@ nsPrintJob::CommonPrint(bool            
 
   return rv;
 }
 
 nsresult
 nsPrintJob::DoCommonPrint(bool                    aIsPrintPreview,
                           nsIPrintSettings*       aPrintSettings,
                           nsIWebProgressListener* aWebProgressListener,
-                          nsIDOMDocument*         aDoc)
+                          nsIDocument*            aDoc)
 {
   nsresult rv;
 
   if (aIsPrintPreview) {
     // The WebProgressListener can be QI'ed to nsIPrintingPromptService
     // then that means the progress dialog is already being shown.
     nsCOMPtr<nsIPrintingPromptService> pps(do_QueryInterface(aWebProgressListener));
     mProgressDialogIsShown = pps != nullptr;
@@ -1027,19 +1026,19 @@ nsPrintJob::DoCommonPrint(bool          
 //---------------------------------------------------------------------------------
 NS_IMETHODIMP
 nsPrintJob::Print(nsIPrintSettings*       aPrintSettings,
                   nsIWebProgressListener* aWebProgressListener)
 {
   // If we have a print preview document, use that instead of the original
   // mDocument. That way animated images etc. get printed using the same state
   // as in print preview.
-  nsCOMPtr<nsIDOMDocument> doc =
-    do_QueryInterface(mPrtPreview && mPrtPreview->mPrintObject ?
-                        mPrtPreview->mPrintObject->mDocument : mDocument);
+  nsIDocument* doc =
+    mPrtPreview && mPrtPreview->mPrintObject ?
+      mPrtPreview->mPrintObject->mDocument : mDocument;
 
   return CommonPrint(false, aPrintSettings, aWebProgressListener, doc);
 }
 
 NS_IMETHODIMP
 nsPrintJob::PrintPreview(nsIPrintSettings* aPrintSettings,
                          mozIDOMWindowProxy* aChildDOMWin,
                          nsIWebProgressListener* aWebProgressListener)
@@ -1056,21 +1055,19 @@ nsPrintJob::PrintPreview(nsIPrintSetting
     FirePrintingErrorEvent(NS_ERROR_GFX_PRINTER_DOC_IS_BUSY);
     return NS_ERROR_FAILURE;
   }
 
   auto* window = nsPIDOMWindowOuter::From(aChildDOMWin);
   NS_ENSURE_STATE(window);
   nsCOMPtr<nsIDocument> doc = window->GetDoc();
   NS_ENSURE_STATE(doc);
-  nsCOMPtr<nsIDOMDocument> domDoc = do_QueryInterface(doc);
-  MOZ_ASSERT(domDoc);
 
   // Document is not busy -- go ahead with the Print Preview
-  return CommonPrint(true, aPrintSettings, aWebProgressListener, domDoc);
+  return CommonPrint(true, aPrintSettings, aWebProgressListener, doc);
 }
 
 //----------------------------------------------------------------------------------
 NS_IMETHODIMP
 nsPrintJob::GetIsFramesetDocument(bool* aIsFramesetDocument)
 {
   nsCOMPtr<nsIDocShell> webContainer(do_QueryReferent(mContainer));
   *aIsFramesetDocument = IsParentAFrameSet(webContainer);
@@ -1405,17 +1402,17 @@ nsPrintJob::BuildDocTree(nsIDocShell*   
     for (int32_t i=0;i<childWebshellCount;i++) {
       nsCOMPtr<nsIDocShellTreeItem> child;
       aParentNode->GetChildAt(i, getter_AddRefs(child));
       nsCOMPtr<nsIDocShell> childAsShell(do_QueryInterface(child));
 
       nsCOMPtr<nsIContentViewer>  viewer;
       childAsShell->GetContentViewer(getter_AddRefs(viewer));
       if (viewer) {
-        nsCOMPtr<nsIDOMDocument> doc = do_GetInterface(childAsShell);
+        nsCOMPtr<nsIDocument> doc = do_GetInterface(childAsShell);
         auto po = MakeUnique<nsPrintObject>();
         po->mParent = aPO.get();
         nsresult rv = po->Init(childAsShell, doc, aPO->mPrintPreview);
         if (NS_FAILED(rv))
           NS_NOTREACHED("Init failed?");
         aPO->mKids.AppendElement(Move(po));
         aDocList->AppendElement(aPO->mKids.LastElement().get());
         BuildDocTree(childAsShell, aDocList, aPO->mKids.LastElement());

--- a/layout/printing/nsPrintJob.h
+++ b/layout/printing/nsPrintJob.h
@@ -191,21 +191,21 @@ public:
 
 private:
   nsPrintJob& operator=(const nsPrintJob& aOther) = delete;
 
   ~nsPrintJob();
 
   nsresult CommonPrint(bool aIsPrintPreview, nsIPrintSettings* aPrintSettings,
                        nsIWebProgressListener* aWebProgressListener,
-                       nsIDOMDocument* aDoc);
+                       nsIDocument* aDoc);
 
   nsresult DoCommonPrint(bool aIsPrintPreview, nsIPrintSettings* aPrintSettings,
                          nsIWebProgressListener* aWebProgressListener,
-                         nsIDOMDocument* aDoc);
+                         nsIDocument* aDoc);
 
   void FirePrintCompletionEvent();
 
   void DisconnectPagePrintTimer();
 
   nsresult AfterNetworkPrint(bool aHandleError);
 
   nsresult SetRootView(nsPrintObject* aPO,

--- a/layout/printing/nsPrintObject.cpp
+++ b/layout/printing/nsPrintObject.cpp
@@ -1,17 +1,16 @@
 /* -*- 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 "nsPrintObject.h"
 #include "nsIContentViewer.h"
-#include "nsIDOMDocument.h"
 #include "nsContentUtils.h" // for nsAutoScriptBlocker
 #include "nsIInterfaceRequestorUtils.h"
 #include "nsPIDOMWindow.h"
 #include "nsGkAtoms.h"
 #include "nsComponentManagerUtils.h"
 #include "nsIDocShellTreeItem.h"
 #include "nsIBaseWindow.h"
 #include "nsIDocument.h"
@@ -41,55 +40,54 @@ nsPrintObject::~nsPrintObject()
     }
   }
   mDocShell = nullptr;
   mTreeOwner = nullptr; // mTreeOwner must be released after mDocShell;
 }
 
 //------------------------------------------------------------------
 nsresult
-nsPrintObject::Init(nsIDocShell* aDocShell, nsIDOMDocument* aDoc,
+nsPrintObject::Init(nsIDocShell* aDocShell, nsIDocument* aDoc,
                     bool aPrintPreview)
 {
+  NS_ENSURE_STATE(aDoc);
+
   mPrintPreview = aPrintPreview;
 
   if (mPrintPreview || mParent) {
     mDocShell = aDocShell;
   } else {
     mTreeOwner = do_GetInterface(aDocShell);
     // Create a container docshell for printing.
     mDocShell = do_CreateInstance("@mozilla.org/docshell;1");
     NS_ENSURE_TRUE(mDocShell, NS_ERROR_OUT_OF_MEMORY);
     mDidCreateDocShell = true;
     mDocShell->SetItemType(aDocShell->ItemType());
     mDocShell->SetTreeOwner(mTreeOwner);
   }
   NS_ENSURE_TRUE(mDocShell, NS_ERROR_FAILURE);
 
   // Keep the document related to this docshell alive
-  nsCOMPtr<nsIDOMDocument> dummy = do_GetInterface(mDocShell);
+  nsCOMPtr<nsIDocument> dummy = do_GetInterface(mDocShell);
   mozilla::Unused << dummy;
 
   nsCOMPtr<nsIContentViewer> viewer;
   mDocShell->GetContentViewer(getter_AddRefs(viewer));
   NS_ENSURE_STATE(viewer);
 
-  nsCOMPtr<nsIDocument> doc = do_QueryInterface(aDoc);
-  NS_ENSURE_STATE(doc);
-
   if (mParent) {
-    nsCOMPtr<nsPIDOMWindowOuter> window = doc->GetWindow();
+    nsCOMPtr<nsPIDOMWindowOuter> window = aDoc->GetWindow();
     if (window) {
       mContent = window->GetFrameElementInternal();
     }
-    mDocument = doc;
+    mDocument = aDoc;
     return NS_OK;
   }
 
-  mDocument = doc->CreateStaticClone(mDocShell);
+  mDocument = aDoc->CreateStaticClone(mDocShell);
   NS_ENSURE_STATE(mDocument);
 
   viewer->SetDocument(mDocument);
   return NS_OK;
 }
 
 //------------------------------------------------------------------
 // Resets PO by destroying the presentation

--- a/layout/printing/nsPrintObject.h
+++ b/layout/printing/nsPrintObject.h
@@ -29,18 +29,17 @@ enum PrintObjectType  {eDoc = 0, eFrame 
 class nsPrintObject
 {
 
 public:
   nsPrintObject();
   ~nsPrintObject(); // non-virtual
 
   // Methods
-  nsresult Init(nsIDocShell* aDocShell, nsIDOMDocument* aDoc,
-                bool aPrintPreview);
+  nsresult Init(nsIDocShell* aDocShell, nsIDocument* aDoc, bool aPrintPreview);
 
   bool IsPrintable()  { return !mDontPrint; }
   void   DestroyPresentation();
 
   // Data Members
   nsCOMPtr<nsIDocShell>    mDocShell;
   nsCOMPtr<nsIDocShellTreeOwner> mTreeOwner;
   nsCOMPtr<nsIDocument>    mDocument;

--- a/layout/xul/nsXULPopupManager.cpp
+++ b/layout/xul/nsXULPopupManager.cpp
@@ -6,17 +6,16 @@
 
 #include "nsGkAtoms.h"
 #include "nsXULPopupManager.h"
 #include "nsMenuFrame.h"
 #include "nsMenuPopupFrame.h"
 #include "nsMenuBarFrame.h"
 #include "nsMenuBarListener.h"
 #include "nsContentUtils.h"
-#include "nsIDOMDocument.h"
 #include "nsXULElement.h"
 #include "nsIDOMXULMenuListElement.h"
 #include "nsIDOMXULCommandDispatcher.h"
 #include "nsCSSFrameConstructor.h"
 #include "nsGlobalWindow.h"
 #include "nsLayoutUtils.h"
 #include "nsViewManager.h"
 #include "nsIComponentManager.h"