diff --git a/dom/base/Selection.cpp b/dom/base/Selection.cpp
index ee5fcb91fd23..ce1c37d8aa71 100644
--- a/dom/base/Selection.cpp
+++ b/dom/base/Selection.cpp
@@ -762,9 +762,8 @@ NS_IMPL_CYCLE_COLLECTION_TRACE_WRAPPERCACHE(Selection)
 // QueryInterface implementation for Selection
 NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(Selection)
   NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
-  NS_INTERFACE_MAP_ENTRY(nsISelection)
   NS_INTERFACE_MAP_ENTRY(nsISupportsWeakReference)
-  NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, nsISelection)
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
 NS_INTERFACE_MAP_END
 
 NS_IMPL_MAIN_THREAD_ONLY_CYCLE_COLLECTING_ADDREF(Selection)
diff --git a/dom/base/Selection.h b/dom/base/Selection.h
index 55210308b4ef..2416fbc39542 100644
--- a/dom/base/Selection.h
+++ b/dom/base/Selection.h
@@ -16,7 +16,6 @@
 #include "mozilla/WeakPtr.h"
 #include "nsDirection.h"
 #include "nsIPresShell.h"  // For ScrollAxis
-#include "nsISelection.h"
 #include "nsISelectionController.h"
 #include "nsISelectionListener.h"
 #include "nsRange.h"
@@ -64,9 +63,8 @@ namespace dom {
 // addreffing/releasing the Selection object is aggregated to nsFrameSelection.
 // Otherwise normal addref/release is used.  This ensures that nsFrameSelection
 // is never deleted before its Selections.
-class Selection final : public nsISelection,
+class Selection final : public nsSupportsWeakReference,
                         public nsWrapperCache,
-                        public nsSupportsWeakReference,
                         public SupportsWeakPtr<Selection>
 {
 protected:
@@ -79,8 +77,7 @@ public:
   MOZ_DECLARE_WEAKREFERENCE_TYPENAME(Selection)
 
   NS_DECL_CYCLE_COLLECTING_ISUPPORTS
-  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS_AMBIGUOUS(Selection, nsISelection)
-  NS_DECL_NSISELECTION
+  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS(Selection)
 
   // match this up with EndbatchChanges. will stop ui updates while multiple
   // selection methods are called
diff --git a/dom/base/moz.build b/dom/base/moz.build
index 47c92071b584..652359a3e64d 100644
--- a/dom/base/moz.build
+++ b/dom/base/moz.build
@@ -25,7 +25,6 @@ XPIDL_SOURCES += [
     'nsIPerformanceMetrics.idl',
     'nsIRemoteWindowContext.idl',
     'nsIScriptChannel.idl',
-    'nsISelection.idl',
     'nsISelectionController.idl',
     'nsISelectionDisplay.idl',
     'nsISelectionListener.idl',
diff --git a/dom/base/nsCopySupport.h b/dom/base/nsCopySupport.h
index dcaa72d84dcc..d87e53bcce4c 100644
--- a/dom/base/nsCopySupport.h
+++ b/dom/base/nsCopySupport.h
@@ -12,7 +12,6 @@
 #include "mozilla/EventForwards.h"
 
 class nsINode;
-class nsISelection;
 class nsIDocument;
 class nsIImageLoadingContent;
 class nsIContent;
diff --git a/dom/base/nsGlobalWindowInner.cpp b/dom/base/nsGlobalWindowInner.cpp
index e1887b473911..cb043a04d979 100644
--- a/dom/base/nsGlobalWindowInner.cpp
+++ b/dom/base/nsGlobalWindowInner.cpp
@@ -121,7 +121,6 @@
 #include "nsView.h"
 #include "nsViewManager.h"
 #include "nsISelectionController.h"
-#include "nsISelection.h"
 #include "nsIPrompt.h"
 #include "nsIPromptService.h"
 #include "nsIPromptFactory.h"
@@ -4432,7 +4431,7 @@ nsGlobalWindowInner::ConvertDialogOptions(const nsAString& aOptions,
 
 void
 nsGlobalWindowInner::UpdateCommands(const nsAString& anAction,
-                                    nsISelection* aSel,
+                                    Selection* aSel,
                                     int16_t aReason)
 {
   if (GetOuterWindowInternal()) {
diff --git a/dom/base/nsGlobalWindowInner.h b/dom/base/nsGlobalWindowInner.h
index e4081868cdf4..75b6ebac2918 100644
--- a/dom/base/nsGlobalWindowInner.h
+++ b/dom/base/nsGlobalWindowInner.h
@@ -897,7 +897,8 @@ public:
              const nsAString& aOptions,
              const mozilla::dom::Sequence<JS::Value>& aExtraArgument,
              mozilla::ErrorResult& aError);
-  void UpdateCommands(const nsAString& anAction, nsISelection* aSel, int16_t aReason);
+  void UpdateCommands(const nsAString& anAction, mozilla::dom::Selection* aSel,
+                      int16_t aReason);
 
   void GetContent(JSContext* aCx,
                   JS::MutableHandle<JSObject*> aRetval,
diff --git a/dom/base/nsGlobalWindowOuter.cpp b/dom/base/nsGlobalWindowOuter.cpp
index 4db07708552e..f33ec565b3d4 100644
--- a/dom/base/nsGlobalWindowOuter.cpp
+++ b/dom/base/nsGlobalWindowOuter.cpp
@@ -118,7 +118,6 @@
 #include "nsView.h"
 #include "nsViewManager.h"
 #include "nsISelectionController.h"
-#include "nsISelection.h"
 #include "nsIPrompt.h"
 #include "nsIPromptService.h"
 #include "nsIPromptFactory.h"
@@ -6275,7 +6274,7 @@ public:
 
 void
 nsGlobalWindowOuter::UpdateCommands(const nsAString& anAction,
-                                    nsISelection* aSel,
+                                    Selection* aSel,
                                     int16_t aReason)
 {
   // If this is a child process, redirect to the parent process.
diff --git a/dom/base/nsGlobalWindowOuter.h b/dom/base/nsGlobalWindowOuter.h
index fb47798c10db..228e932b8bbc 100644
--- a/dom/base/nsGlobalWindowOuter.h
+++ b/dom/base/nsGlobalWindowOuter.h
@@ -692,7 +692,8 @@ public:
                       const nsAString& aOptions,
                       nsISupports* aExtraArgument,
                       nsPIDOMWindowOuter** _retval) override;
-  void UpdateCommands(const nsAString& anAction, nsISelection* aSel, int16_t aReason) override;
+  void UpdateCommands(const nsAString& anAction, mozilla::dom::Selection* aSel,
+                      int16_t aReason) override;
 
   already_AddRefed<nsPIDOMWindowOuter>
   GetContentInternal(mozilla::ErrorResult& aError,
diff --git a/dom/base/nsISelection.idl b/dom/base/nsISelection.idl
deleted file mode 100644
index 84440ae25639..000000000000
--- a/dom/base/nsISelection.idl
+++ /dev/null
@@ -1,31 +0,0 @@
-/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
-/* 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"
-
-/* THIS IS A PUBLIC INTERFACE */
-
-interface nsIDOMNode;
-interface nsINode;
-
-%{C++
-namespace mozilla {
-namespace dom {
-class Selection;
-} // namespace dom
-} // namespace mozilla
-%}
-
-/**
- * Interface for manipulating and querying the current selected range
- * of nodes within the document.
- *
- * @version 1.0
- */
-
-[shim(Selection), uuid(e0a4d4b3-f34e-44bd-b1f2-4e3bde9b6915)]
-interface nsISelection : nsISupports
-{
-};
diff --git a/dom/base/nsPIDOMWindow.h b/dom/base/nsPIDOMWindow.h
index 389801c6ba60..0a1102786cd1 100644
--- a/dom/base/nsPIDOMWindow.h
+++ b/dom/base/nsPIDOMWindow.h
@@ -32,7 +32,6 @@ class nsIDocShellLoadInfo;
 class nsIDocument;
 class nsIIdleObserver;
 class nsIPrincipal;
-class nsISelection;
 class nsIScriptTimeoutHandler;
 class nsISerialEventTarget;
 class nsIURI;
@@ -1120,7 +1119,9 @@ public:
 
   virtual nsresult MoveBy(int32_t aXDif, int32_t aYDif) = 0;
 
-  virtual void UpdateCommands(const nsAString& anAction, nsISelection* aSel, int16_t aReason) = 0;
+  virtual void UpdateCommands(const nsAString& anAction,
+                              mozilla::dom::Selection* aSel,
+                              int16_t aReason) = 0;
 
   mozilla::dom::DocGroup* GetDocGroup() const;
   virtual nsISerialEventTarget*
diff --git a/dom/events/IMEContentObserver.h b/dom/events/IMEContentObserver.h
index 1852f268b475..b0d697bf5433 100644
--- a/dom/events/IMEContentObserver.h
+++ b/dom/events/IMEContentObserver.h
@@ -23,7 +23,6 @@
 
 class nsIContent;
 class nsINode;
-class nsISelection;
 class nsPresContext;
 
 namespace mozilla {
diff --git a/dom/events/IMEStateManager.cpp b/dom/events/IMEStateManager.cpp
index 105b69267ed6..fc0d59e2b332 100644
--- a/dom/events/IMEStateManager.cpp
+++ b/dom/events/IMEStateManager.cpp
@@ -34,7 +34,6 @@
 #include "nsINode.h"
 #include "nsIObserverService.h"
 #include "nsIPresShell.h"
-#include "nsISelection.h"
 #include "nsISupports.h"
 #include "nsPresContext.h"
 
diff --git a/dom/events/IMEStateManager.h b/dom/events/IMEStateManager.h
index a39fb2295bd1..1d2bd99586b4 100644
--- a/dom/events/IMEStateManager.h
+++ b/dom/events/IMEStateManager.h
@@ -15,7 +15,6 @@
 class nsIContent;
 class nsINode;
 class nsPresContext;
-class nsISelection;
 
 namespace mozilla {
 
diff --git a/dom/html/TextInputListener.h b/dom/html/TextInputListener.h
index 8681684bd6d7..b043b82a3d41 100644
--- a/dom/html/TextInputListener.h
+++ b/dom/html/TextInputListener.h
@@ -13,12 +13,15 @@
 #include "nsWeakReference.h"
 
 class nsIFrame;
-class nsISelection;
 class nsITextControlElement;
 class nsTextControlFrame;
 
 namespace mozilla {
 
+namespace dom {
+class Selection;
+} // namespace dom
+
 class TextInputListener final : public nsIDOMEventListener
                               , public nsSupportsWeakReference
 {
@@ -75,7 +78,7 @@ protected:
   virtual ~TextInputListener() = default;
 
   nsresult UpdateTextInputCommands(const nsAString& aCommandsToUpdate,
-                                   nsISelection* aSelection = nullptr,
+                                   dom::Selection* aSelection = nullptr,
                                    int16_t aReason = 0);
 
 protected:
diff --git a/dom/html/nsTextEditorState.cpp b/dom/html/nsTextEditorState.cpp
index f93826c9864b..a0e61c588c96 100644
--- a/dom/html/nsTextEditorState.cpp
+++ b/dom/html/nsTextEditorState.cpp
@@ -1029,7 +1029,7 @@ TextInputListener::HandleValueChanged(nsTextControlFrame* aFrame)
 
 nsresult
 TextInputListener::UpdateTextInputCommands(const nsAString& aCommandsToUpdate,
-                                           nsISelection* aSelection,
+                                           Selection* aSelection,
                                            int16_t aReason)
 {
   nsIContent* content = mFrame->GetContent();
diff --git a/editor/composer/ComposerCommandsUpdater.cpp b/editor/composer/ComposerCommandsUpdater.cpp
index 4a8f74305880..974225bb1f27 100644
--- a/editor/composer/ComposerCommandsUpdater.cpp
+++ b/editor/composer/ComposerCommandsUpdater.cpp
@@ -18,7 +18,6 @@
 #include "nsIDOMWindow.h"               // for nsIDOMWindow
 #include "nsIDocShell.h"                // for nsIDocShell
 #include "nsIInterfaceRequestorUtils.h"  // for do_GetInterface
-#include "nsISelection.h"               // for nsISelection
 #include "nsITransactionManager.h"      // for nsITransactionManager
 #include "nsLiteralString.h"            // for NS_LITERAL_STRING
 #include "nsPICommandUpdater.h"         // for nsPICommandUpdater
diff --git a/editor/composer/nsEditingSession.cpp b/editor/composer/nsEditingSession.cpp
index daff8036bd71..03212a758560 100644
--- a/editor/composer/nsEditingSession.cpp
+++ b/editor/composer/nsEditingSession.cpp
@@ -36,7 +36,6 @@
 #include "nsIPresShell.h"               // for nsIPresShell
 #include "nsIRefreshURI.h"              // for nsIRefreshURI
 #include "nsIRequest.h"                 // for nsIRequest
-#include "nsISelection.h"               // for nsISelection
 #include "nsITimer.h"                   // for nsITimer, etc
 #include "nsITransactionManager.h"      // for nsITransactionManager
 #include "nsIWeakReference.h"           // for nsISupportsWeakReference, etc
diff --git a/editor/libeditor/HTMLAnonymousNodeEditor.cpp b/editor/libeditor/HTMLAnonymousNodeEditor.cpp
index a1fce16e6b53..643b8bd99fa6 100644
--- a/editor/libeditor/HTMLAnonymousNodeEditor.cpp
+++ b/editor/libeditor/HTMLAnonymousNodeEditor.cpp
@@ -41,7 +41,6 @@
 #include "nsROCSSPrimitiveValue.h"
 
 class nsIDOMEventListener;
-class nsISelection;
 
 namespace mozilla {
 
diff --git a/editor/libeditor/HTMLEditor.h b/editor/libeditor/HTMLEditor.h
index b64896ad7a35..48aa9f6de45d 100644
--- a/editor/libeditor/HTMLEditor.h
+++ b/editor/libeditor/HTMLEditor.h
@@ -43,7 +43,6 @@ class nsILinkHandler;
 class nsTableWrapperFrame;
 class nsIDOMRange;
 class nsRange;
-class nsISelection;
 
 namespace mozilla {
 class AutoSelectionSetterAfterTableEdit;
diff --git a/editor/libeditor/HTMLEditorObjectResizer.cpp b/editor/libeditor/HTMLEditorObjectResizer.cpp
index 610f7b2a62d3..907b051629a1 100644
--- a/editor/libeditor/HTMLEditorObjectResizer.cpp
+++ b/editor/libeditor/HTMLEditorObjectResizer.cpp
@@ -35,8 +35,6 @@
 #include "nscore.h"
 #include <algorithm>
 
-class nsISelection;
-
 namespace mozilla {
 
 using namespace dom;
diff --git a/editor/spellchecker/TextServicesDocument.h b/editor/spellchecker/TextServicesDocument.h
index acc159e619a1..b59378840b85 100644
--- a/editor/spellchecker/TextServicesDocument.h
+++ b/editor/spellchecker/TextServicesDocument.h
@@ -19,7 +19,6 @@ class nsIContentIterator;
 class nsIDOMNode;
 class nsIEditor;
 class nsINode;
-class nsISelection;
 class nsISelectionController;
 class nsITextServicesFilter;
 class nsRange;
diff --git a/extensions/spellcheck/src/mozInlineSpellChecker.cpp b/extensions/spellcheck/src/mozInlineSpellChecker.cpp
index dc052c528ad8..b5278fde4259 100644
--- a/extensions/spellcheck/src/mozInlineSpellChecker.cpp
+++ b/extensions/spellcheck/src/mozInlineSpellChecker.cpp
@@ -56,7 +56,6 @@
 #include "nsIPrefBranch.h"
 #include "nsIPrefService.h"
 #include "nsIRunnable.h"
-#include "nsISelection.h"
 #include "nsISelectionController.h"
 #include "nsIServiceManager.h"
 #include "nsITextServicesFilter.h"
diff --git a/layout/base/nsCaret.h b/layout/base/nsCaret.h
index e61ae16c1960..5ed255a9f80f 100644
--- a/layout/base/nsCaret.h
+++ b/layout/base/nsCaret.h
@@ -75,7 +75,7 @@ class nsCaret final : public nsISelectionListener
      *  It does not take account of blinking or the caret being hidden
      *  because we're in non-editable/disabled content.
      */
-    bool IsVisible(nsISelection* aSelection = nullptr)
+    bool IsVisible(mozilla::dom::Selection* aSelection = nullptr)
     {
       if (!mVisible || mHideCount) {
         return false;
@@ -84,7 +84,7 @@ class nsCaret final : public nsISelectionListener
       if (!mShowDuringSelection) {
         mozilla::dom::Selection* selection;
         if (aSelection) {
-          selection = static_cast<mozilla::dom::Selection*>(aSelection);
+          selection = aSelection;
         } else {
           selection = GetSelection();
         }
diff --git a/layout/base/nsIPresShell.h b/layout/base/nsIPresShell.h
index e136590c6bcb..f09a058dca05 100644
--- a/layout/base/nsIPresShell.h
+++ b/layout/base/nsIPresShell.h
@@ -65,7 +65,6 @@ class nsILayoutHistoryState;
 class nsIReflowCallback;
 class nsIDOMNode;
 class nsCSSFrameConstructor;
-class nsISelection;
 template<class E> class nsCOMArray;
 class AutoWeakFrame;
 class WeakFrame;
diff --git a/layout/forms/nsTextControlFrame.cpp b/layout/forms/nsTextControlFrame.cpp
index c078fc70b5ac..ba0060b2d6ca 100644
--- a/layout/forms/nsTextControlFrame.cpp
+++ b/layout/forms/nsTextControlFrame.cpp
@@ -774,7 +774,7 @@ void nsTextControlFrame::SetFocus(bool aOn, bool aRepaint)
   }
 
   // Scroll the current selection into view
-  nsISelection *caretSelection = caret->GetSelection();
+  Selection* caretSelection = caret->GetSelection();
   const bool isFocusedRightNow = ourSel == caretSelection;
   if (!isFocusedRightNow) {
     // Don't scroll the current selection if we've been focused using the mouse.
diff --git a/layout/generic/nsFrameSelection.cpp b/layout/generic/nsFrameSelection.cpp
index c5c9d5d6ec3e..bcdf13b11a10 100644
--- a/layout/generic/nsFrameSelection.cpp
+++ b/layout/generic/nsFrameSelection.cpp
@@ -2936,7 +2936,7 @@ NS_IMPL_ISUPPORTS(nsAutoCopyListener, nsISelectionListener)
  * What we should do, to make our end of the deal faster:
  * Create a singleton transferable with our own magic converter.  When selection
  * changes (use a quick cache to detect ``real'' changes), we put the new
- * nsISelection in the transferable.  Our magic converter will take care of
+ * Selection in the transferable.  Our magic converter will take care of
  * transferable->whatever-other-format when the time comes to actually
  * hand over the clipboard contents.
  *
diff --git a/mobile/android/modules/ActionBarHandler.jsm b/mobile/android/modules/ActionBarHandler.jsm
index 1a02029735a2..9c5141b57178 100644
--- a/mobile/android/modules/ActionBarHandler.jsm
+++ b/mobile/android/modules/ActionBarHandler.jsm
@@ -757,7 +757,7 @@ var ActionBarHandler = {
   },
 
   /**
-   * Provides the nsISelection for either an editor, or from the
+   * Provides the Selection for either an editor, or from the
    * default window.
    */
   _getSelection: function(element = this._targetElement, win = this._contentWindow) {
diff --git a/toolkit/components/find/nsFind.cpp b/toolkit/components/find/nsFind.cpp
index efbe9b1fcf87..fba275210b21 100644
--- a/toolkit/components/find/nsFind.cpp
+++ b/toolkit/components/find/nsFind.cpp
@@ -10,7 +10,6 @@
 #include "nsContentCID.h"
 #include "nsIContent.h"
 #include "nsIDOMNode.h"
-#include "nsISelection.h"
 #include "nsISelectionController.h"
 #include "nsIFrame.h"
 #include "nsITextControlFrame.h"
diff --git a/toolkit/components/typeaheadfind/nsTypeAheadFind.h b/toolkit/components/typeaheadfind/nsTypeAheadFind.h
index ce8696b1b3c5..c45c155e58e4 100644
--- a/toolkit/components/typeaheadfind/nsTypeAheadFind.h
+++ b/toolkit/components/typeaheadfind/nsTypeAheadFind.h
@@ -13,7 +13,6 @@
 #include "nsIFind.h"
 #include "nsIWebBrowserFind.h"
 #include "nsWeakReference.h"
-#include "nsISelection.h"
 #include "nsIDOMRange.h"
 #include "nsIDocShellTreeItem.h"
 #include "nsITypeAheadFind.h"
diff --git a/widget/android/GeckoEditableSupport.cpp b/widget/android/GeckoEditableSupport.cpp
index 3424f0aa25a1..55e0987face4 100644
--- a/widget/android/GeckoEditableSupport.cpp
+++ b/widget/android/GeckoEditableSupport.cpp
@@ -10,7 +10,6 @@
 #include "KeyEvent.h"
 #include "PuppetWidget.h"
 #include "nsIContent.h"
-#include "nsISelection.h"
 
 #include "mozilla/IMEStateManager.h"
 #include "mozilla/Preferences.h"
diff --git a/widget/gtk/nsDragService.cpp b/widget/gtk/nsDragService.cpp
index 7a6ad8616b40..72ea10cf3c99 100644
--- a/widget/gtk/nsDragService.cpp
+++ b/widget/gtk/nsDragService.cpp
@@ -34,7 +34,6 @@
 #include "nsPresContext.h"
 #include "nsIContent.h"
 #include "nsIDocument.h"
-#include "nsISelection.h"
 #include "nsViewManager.h"
 #include "nsIFrame.h"
 #include "nsGtkUtils.h"