--- a/layout/base/moz.build
+++ b/layout/base/moz.build
@@ -15,16 +15,17 @@ with Files('nsChangeHint.h'):
 
 with Files('nsBidi*'):
     BUG_COMPONENT = ('Core', 'Layout: Text')
 
 with Files('AccessibleCaret*'):
     BUG_COMPONENT = ('Core', 'Selection')
 
 XPIDL_SOURCES += [
+    'nsILayoutHistoryState.idl',
     'nsIPreloadedStyleSheet.idl',
     'nsIStyleSheetService.idl',
 ]
 
 if CONFIG['MOZ_DEBUG']:
     UNIFIED_SOURCES += [
         'nsAutoLayoutPhase.cpp',
     ]
@@ -42,17 +43,16 @@ EXPORTS += [
     'nsChangeHint.h',
     'nsCompatibility.h',
     'nsCSSFrameConstructor.h',
     'nsFrameManager.h',
     'nsFrameManagerBase.h',
     'nsFrameTraversal.h',
     'nsIFrameTraversal.h',
     'nsILayoutDebugger.h',
-    'nsILayoutHistoryState.h',
     'nsIPercentBSizeObserver.h',
     'nsIPresShell.h',
     'nsIPresShellInlines.h',
     'nsIReflowCallback.h',
     'nsLayoutUtils.h',
     'nsPresArena.h',
     'nsPresArenaObjectList.h',
     'nsPresContext.h',

rename from layout/base/nsILayoutHistoryState.h
rename to layout/base/nsILayoutHistoryState.idl
--- a/layout/base/nsILayoutHistoryState.h
+++ b/layout/base/nsILayoutHistoryState.idl
@@ -1,70 +1,70 @@
-/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* -*- 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/. */
 
 /*
  * interface for container for information saved in session history when
  * the document is not
  */
 
-#ifndef _nsILayoutHistoryState_h
-#define _nsILayoutHistoryState_h
+#include "nsISupports.idl"
+
+interface nsPresState;
 
-#include "nsISupports.h"
+[ptr] native nsPresStatePtr(nsPresState);
+[ref] native nsCString(const nsCString);
+native constBool(const bool);
+
+%{C++
 #include "nsStringFwd.h"
 
-class nsPresState;
 template<typename> struct already_AddRefed;
+%}
 
-#define NS_ILAYOUTHISTORYSTATE_IID \
-{ 0xaef27cb3, 0x4df9, 0x4eeb, \
-  { 0xb0, 0xb0, 0xac, 0x56, 0xcf, 0x86, 0x1d, 0x04 } }
-
-class nsILayoutHistoryState : public nsISupports {
- public: 
-  NS_DECLARE_STATIC_IID_ACCESSOR(NS_ILAYOUTHISTORYSTATE_IID)
+[uuid(aef27cb3-4df9-4eeb-b0b0-ac56cf861d04)]
+interface nsILayoutHistoryState : nsISupports
+{
+  // Native only interface, converted from the original nsILayoutHistoryState.h
 
   /**
    * Set |aState| as the state object for |aKey|.
    * This _transfers_ownership_ of |aState| to the LayoutHistoryState.
    * It will be freed when RemoveState() is called or when the
    * LayoutHistoryState is destroyed.
    */
-  virtual void AddState(const nsCString& aKey, nsPresState* aState) = 0;
+  [noscript, notxpcom, nostdcall] void AddState(in nsCString aKey, in nsPresStatePtr aState);
 
   /**
    * Look up the state object for |aKey|.
    */
-  virtual nsPresState* GetState(const nsCString& aKey) = 0;
+  [noscript, notxpcom, nostdcall] nsPresStatePtr GetState(in nsCString aKey);
 
   /**
    * Remove the state object for |aKey|.
    */
-  virtual void RemoveState(const nsCString& aKey) = 0;
+  [noscript, notxpcom, nostdcall] void RemoveState(in nsCString aKey);
 
   /**
    * Check whether this history has any states in it
    */
-  virtual bool HasStates() const = 0;
+  [noscript, notxpcom, nostdcall] boolean HasStates();
 
   /**
    * Sets whether this history can contain only scroll position history
    * or all possible history
    */
-  virtual void SetScrollPositionOnly(const bool aFlag) = 0;
+  [noscript, notxpcom, nostdcall] void SetScrollPositionOnly(in constBool aFlag);
 
   /**
    * Resets nsPresState::GetScrollState of all nsPresState objects to 0,0.
    */
-  virtual void ResetScrollState() = 0;
+  [noscript, notxpcom, nostdcall] void ResetScrollState();
 };
 
-NS_DEFINE_STATIC_IID_ACCESSOR(nsILayoutHistoryState,
-                              NS_ILAYOUTHISTORYSTATE_IID)
-
+%{C++
 already_AddRefed<nsILayoutHistoryState>
 NS_NewLayoutHistoryState();
+%}
 
-#endif /* _nsILayoutHistoryState_h */
 

--- a/layout/base/nsLayoutHistoryState.cpp
+++ b/layout/base/nsLayoutHistoryState.cpp
@@ -19,30 +19,17 @@ class nsLayoutHistoryState final : publi
 {
 public:
   nsLayoutHistoryState()
     : mScrollPositionOnly(false)
   {
   }
 
   NS_DECL_ISUPPORTS
-
-  // nsILayoutHistoryState
-  virtual void
-  AddState(const nsCString& aKey, nsPresState* aState) override;
-  virtual nsPresState*
-  GetState(const nsCString& aKey) override;
-  virtual void
-  RemoveState(const nsCString& aKey) override;
-  virtual bool
-  HasStates() const override;
-  virtual void
-  SetScrollPositionOnly(const bool aFlag) override;
-  virtual void
-  ResetScrollState() override;
+  NS_DECL_NSILAYOUTHISTORYSTATE
 
 private:
   ~nsLayoutHistoryState() {}
   bool mScrollPositionOnly;
 
   nsClassHashtable<nsCStringHashKey,nsPresState> mStates;
 };
 
@@ -80,17 +67,17 @@ nsLayoutHistoryState::GetState(const nsC
 
 void
 nsLayoutHistoryState::RemoveState(const nsCString& aKey)
 {
   mStates.Remove(aKey);
 }
 
 bool
-nsLayoutHistoryState::HasStates() const
+nsLayoutHistoryState::HasStates()
 {
   return mStates.Count() != 0;
 }
 
 void
 nsLayoutHistoryState::SetScrollPositionOnly(const bool aFlag)
 {
   mScrollPositionOnly = aFlag;