deleted file mode 100644
--- a/layout/base/ArenaRefPtr.h
+++ /dev/null
@@ -1,162 +0,0 @@
-/* -*- 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/.
- */
-
-/* smart pointer for strong references to nsPresArena-allocated objects
-   that might be held onto until the arena's destruction */
-
-#include "mozilla/Assertions.h"
-#include "mozilla/RefPtr.h"
-
-#ifndef mozilla_ArenaRefPtr_h
-#define mozilla_ArenaRefPtr_h
-
-class nsPresArena;
-
-namespace mozilla {
-
-/**
- * A class for holding strong references to nsPresArena-allocated
- * objects.
- *
- * Since the arena's lifetime is not related to the refcounts
- * of the objects allocated within it, it is possible to have a strong
- * reference to an arena-allocated object that lives until the
- * destruction of the arena.  An ArenaRefPtr acts like a weak reference
- * in that it will clear its referent if the arena is about to go away.
- *
- * T must be a class that has these two methods:
- *
- *   static mozilla::ArenaObjectID ArenaObjectID();
- *   U* Arena();
- *
- * where U is a class that has these two methods:
- *
- *   void RegisterArenaRefPtr(ArenaRefPtr<T>*);
- *   void DeregisterArenaRefPtr(ArenaRefPtr<T>*);
- *
- * Currently, both nsPresArena and nsIPresShell can be used as U.
- *
- * The ArenaObjectID method must return the mozilla::ArenaObjectID that
- * uniquely identifies T, and the Arena method must return the nsPresArena
- * (or a proxy for it) in which the object was allocated.
- */
-template<typename T>
-class ArenaRefPtr
-{
-  friend class ::nsPresArena;
-
-public:
-  ArenaRefPtr()
-  {
-    AssertValidType();
-  }
-
-  template<typename I>
-  MOZ_IMPLICIT ArenaRefPtr(already_AddRefed<I>& aRhs)
-  {
-    AssertValidType();
-    assign(aRhs);
-  }
-
-  template<typename I>
-  MOZ_IMPLICIT ArenaRefPtr(already_AddRefed<I>&& aRhs)
-  {
-    AssertValidType();
-    assign(aRhs);
-  }
-
-  MOZ_IMPLICIT ArenaRefPtr(T* aRhs)
-  {
-    AssertValidType();
-    assign(aRhs);
-  }
-
-  template<typename I>
-  ArenaRefPtr<T>& operator=(already_AddRefed<I>& aRhs)
-  {
-    assign(aRhs);
-    return *this;
-  }
-
-  template<typename I>
-  ArenaRefPtr<T>& operator=(already_AddRefed<I>&& aRhs)
-  {
-    assign(aRhs);
-    return *this;
-  }
-
-  ArenaRefPtr<T>& operator=(T* aRhs)
-  {
-    assign(aRhs);
-    return *this;
-  }
-
-  ~ArenaRefPtr() { assign(nullptr); }
-
-  operator T*() const & { return get(); }
-  operator T*() const && = delete;
-  explicit operator bool() const { return !!mPtr; }
-  bool operator!() const { return !mPtr; }
-  T* operator->() const { return mPtr.operator->(); }
-  T& operator*() const { return *get(); }
-
-  T* get() const { return mPtr; }
-
-private:
-  void AssertValidType();
-
-  /**
-   * Clears the pointer to the arena-allocated object but skips the usual
-   * step of deregistering the ArenaRefPtr from the nsPresArena.  This
-   * method is called by nsPresArena when clearing all registered ArenaRefPtrs
-   * so that it can deregister them all at once, avoiding hash table churn.
-   */
-  void ClearWithoutDeregistering()
-  {
-    mPtr = nullptr;
-  }
-
-  template<typename I>
-  void assign(already_AddRefed<I>& aSmartPtr)
-  {
-    RefPtr<T> newPtr(aSmartPtr);
-    assignFrom(newPtr);
-  }
-
-  template<typename I>
-  void assign(already_AddRefed<I>&& aSmartPtr)
-  {
-    RefPtr<T> newPtr(aSmartPtr);
-    assignFrom(newPtr);
-  }
-
-  void assign(T* aPtr) { assignFrom(aPtr); }
-
-  template<typename I>
-  void assignFrom(I& aPtr)
-  {
-    if (aPtr == mPtr) {
-      return;
-    }
-    bool sameArena = mPtr && aPtr && mPtr->Arena() == aPtr->Arena();
-    if (mPtr && !sameArena) {
-      MOZ_ASSERT(mPtr->Arena());
-      mPtr->Arena()->DeregisterArenaRefPtr(this);
-    }
-    mPtr = Move(aPtr);
-    if (mPtr && !sameArena) {
-      MOZ_ASSERT(mPtr->Arena());
-      mPtr->Arena()->RegisterArenaRefPtr(this);
-    }
-  }
-
-  RefPtr<T> mPtr;
-};
-
-} // namespace mozilla
-
-#endif // mozilla_ArenaRefPtr_h

deleted file mode 100644
--- a/layout/base/ArenaRefPtrInlines.h
+++ /dev/null
@@ -1,44 +0,0 @@
-/* -*- 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/.
- */
-
-/* inline methods that belong in ArenaRefPtr.h, except that they require
-   the inclusion of headers for all types that ArenaRefPtr can handle */
-
-#ifndef mozilla_ArenaRefPtrInlines_h
-#define mozilla_ArenaRefPtrInlines_h
-
-#include "mozilla/ArenaObjectID.h"
-#include "mozilla/Assertions.h"
-#include "mozilla/ComputedStyle.h"
-#include "nsStyleStruct.h"
-
-namespace mozilla {
-
-template<typename T>
-void
-ArenaRefPtr<T>::AssertValidType()
-{
-  // If adding new types, please update nsPresArena::ClearArenaRefPtrWithoutDeregistering
-  // as well
-  static_assert(IsSame<T, ComputedStyle>::value,
-                "ArenaRefPtr<T> template parameter T must be declared in "
-                "nsPresArenaObjectList and explicitly handled in"
-                "nsPresArena.cpp");
-}
-
-} // namespace mozilla
-
-template<typename T>
-void
-nsPresArena::RegisterArenaRefPtr(mozilla::ArenaRefPtr<T>* aPtr)
-{
-  MOZ_ASSERT(!mArenaRefPtrs.Contains(aPtr));
-  mArenaRefPtrs.Put(aPtr, T::ArenaObjectID());
-}
-
-
-#endif

--- a/layout/base/PresShell.cpp
+++ b/layout/base/PresShell.cpp
@@ -1327,33 +1327,16 @@ PresShell::Destroy()
 
   if (mViewManager) {
     // Clear the view manager's weak pointer back to |this| in case it
     // was leaked.
     mViewManager->SetPresShell(nullptr);
     mViewManager = nullptr;
   }
 
-  // mFrameArena will be destroyed soon.  Clear out any ArenaRefPtrs
-  // pointing to objects in the arena now.  This is done:
-  //
-  //   (a) before mFrameArena's destructor runs so that our
-  //       mAllocatedPointers becomes empty and doesn't trip the assertion
-  //       in ~PresShell,
-  //   (b) before the mPresContext->DetachShell() below, so
-  //       that when we clear the ArenaRefPtrs they'll still be able to
-  //       get back to this PresShell to deregister themselves (e.g. note
-  //       how ComputedStyle::Arena returns the PresShell got from its
-  //       rule node's nsPresContext, which would return null if we'd already
-  //       called mPresContext->DetachShell()), and
-  //   (c) before the mStyleSet->BeginShutdown() call just below, so that
-  //       the ComputedStyles don't complain they're being destroyed later
-  //       than the rule tree is.
-  mFrameArena.ClearArenaRefPtrs();
-
   mStyleSet->BeginShutdown();
   nsRefreshDriver* rd = GetPresContext()->RefreshDriver();
 
   // This shell must be removed from the document before the frame
   // hierarchy is torn down to avoid finding deleted frames through
   // this presshell while the frames are being torn down
   if (mDocument) {
     NS_ASSERTION(mDocument->GetShell() == this, "Wrong shell?");

--- a/layout/base/moz.build
+++ b/layout/base/moz.build
@@ -69,18 +69,16 @@ EXPORTS += [
     'Units.h',
     'UnitTransforms.h',
     'WordMovementType.h',
     'ZoomConstraintsClient.h',
 ]
 
 EXPORTS.mozilla += [
     'ArenaObjectID.h',
-    'ArenaRefPtr.h',
-    'ArenaRefPtrInlines.h',
     'GeometryUtils.h',
     'OverflowChangedTracker.h',
     'PresShell.h',
     'RestyleLogging.h',
     'RestyleManager.h',
     'RestyleManagerInlines.h',
     'ServoRestyleManager.h',
     'ShapeUtils.h',

--- a/layout/base/nsIPresShell.h
+++ b/layout/base/nsIPresShell.h
@@ -230,33 +230,16 @@ public:
 
   void FreeByObjectID(mozilla::ArenaObjectID aID, void* aPtr)
   {
     RecordFree(aPtr);
     if (!mIsDestroying)
       mFrameArena.FreeByObjectID(aID, aPtr);
   }
 
-  template<typename T>
-  void RegisterArenaRefPtr(mozilla::ArenaRefPtr<T>* aPtr)
-  {
-    mFrameArena.RegisterArenaRefPtr(aPtr);
-  }
-
-  template<typename T>
-  void DeregisterArenaRefPtr(mozilla::ArenaRefPtr<T>* aPtr)
-  {
-    mFrameArena.DeregisterArenaRefPtr(aPtr);
-  }
-
-  void ClearArenaRefPtrs(mozilla::ArenaObjectID aObjectID)
-  {
-    mFrameArena.ClearArenaRefPtrs(aObjectID);
-  }
-
   nsIDocument* GetDocument() const { return mDocument; }
 
   nsPresContext* GetPresContext() const { return mPresContext; }
 
   nsViewManager* GetViewManager() const { return mViewManager; }
 
   nsRefreshDriver* GetRefreshDriver() const;
 

--- a/layout/base/nsPresArena.cpp
+++ b/layout/base/nsPresArena.cpp
@@ -23,71 +23,28 @@
 using namespace mozilla;
 
 nsPresArena::nsPresArena()
 {
 }
 
 nsPresArena::~nsPresArena()
 {
-  ClearArenaRefPtrs();
-
 #if defined(MOZ_HAVE_MEM_CHECKS)
   for (FreeList* entry = mFreeLists; entry != ArrayEnd(mFreeLists); ++entry) {
     nsTArray<void*>::index_type len;
     while ((len = entry->mEntries.Length())) {
       void* result = entry->mEntries.ElementAt(len - 1);
       entry->mEntries.RemoveElementAt(len - 1);
       MOZ_MAKE_MEM_UNDEFINED(result, entry->mEntrySize);
     }
   }
 #endif
 }
 
-/* inline */ void
-nsPresArena::ClearArenaRefPtrWithoutDeregistering(void* aPtr,
-                                                  ArenaObjectID aObjectID)
-{
-  switch (aObjectID) {
-    // We use ArenaRefPtr<ComputedStyle>, which can be ComputedStyle
-    // or GeckoComputedStyle. GeckoComputedStyle is actually arena managed,
-    // but ComputedStyle isn't.
-    case eArenaObjectID_GeckoComputedStyle:
-      static_cast<ArenaRefPtr<ComputedStyle>*>(aPtr)->ClearWithoutDeregistering();
-      return;
-    default:
-      MOZ_ASSERT(false, "unexpected ArenaObjectID value");
-      break;
-  }
-}
-
-void
-nsPresArena::ClearArenaRefPtrs()
-{
-  for (auto iter = mArenaRefPtrs.Iter(); !iter.Done(); iter.Next()) {
-    void* ptr = iter.Key();
-    ArenaObjectID id = iter.UserData();
-    ClearArenaRefPtrWithoutDeregistering(ptr, id);
-  }
-  mArenaRefPtrs.Clear();
-}
-
-void
-nsPresArena::ClearArenaRefPtrs(ArenaObjectID aObjectID)
-{
-  for (auto iter = mArenaRefPtrs.Iter(); !iter.Done(); iter.Next()) {
-    void* ptr = iter.Key();
-    ArenaObjectID id = iter.UserData();
-    if (id == aObjectID) {
-      ClearArenaRefPtrWithoutDeregistering(ptr, id);
-      iter.Remove();
-    }
-  }
-}
-
 void*
 nsPresArena::Allocate(uint32_t aCode, size_t aSize)
 {
   MOZ_ASSERT(aSize > 0, "PresArena cannot allocate zero bytes");
   MOZ_ASSERT(aCode < ArrayLength(mFreeLists));
 
   // We only hand out aligned sizes
   aSize = mPool.AlignedSize(aSize);

--- a/layout/base/nsPresArena.h
+++ b/layout/base/nsPresArena.h
@@ -7,17 +7,16 @@
 
 /* arena allocation for the frame tree and closely-related objects */
 
 #ifndef nsPresArena_h___
 #define nsPresArena_h___
 
 #include "mozilla/ArenaAllocator.h"
 #include "mozilla/ArenaObjectID.h"
-#include "mozilla/ArenaRefPtr.h"
 #include "mozilla/Assertions.h"
 #include "mozilla/MemoryChecking.h" // Note: Do not remove this, needed for MOZ_HAVE_MEM_CHECKS below
 #include "mozilla/MemoryReporting.h"
 #include <stdint.h>
 #include "nscore.h"
 #include "nsDataHashtable.h"
 #include "nsHashKeys.h"
 #include "nsTArray.h"
@@ -61,55 +60,16 @@ public:
     return Allocate(aID, aSize);
   }
   void FreeByCustomID(uint32_t aID, void* ptr)
   {
     Free(aID, ptr);
   }
 
   /**
-   * Register an ArenaRefPtr to be cleared when this arena is about to
-   * be destroyed.
-   *
-   * (Defined in ArenaRefPtrInlines.h.)
-   *
-   * @param aPtr The ArenaRefPtr to clear.
-   * @param aObjectID The ArenaObjectID value that uniquely identifies
-   *   the type of object the ArenaRefPtr holds.
-   */
-  template<typename T>
-  void RegisterArenaRefPtr(mozilla::ArenaRefPtr<T>* aPtr);
-
-  /**
-   * Deregister an ArenaRefPtr that was previously registered with
-   * RegisterArenaRefPtr.
-   */
-  template<typename T>
-  void DeregisterArenaRefPtr(mozilla::ArenaRefPtr<T>* aPtr)
-  {
-    MOZ_ASSERT(mArenaRefPtrs.Contains(aPtr));
-    mArenaRefPtrs.Remove(aPtr);
-  }
-
-  /**
-   * Clears all currently registered ArenaRefPtrs.  This will be called during
-   * the destructor, but can be called by users of nsPresArena who want to
-   * ensure arena-allocated objects are released earlier.
-   */
-  void ClearArenaRefPtrs();
-
-  /**
-   * Clears all currently registered ArenaRefPtrs for the given ArenaObjectID.
-   * This is called when we reconstruct the rule tree so that style contexts
-   * pointing into the old rule tree aren't released afterwards, triggering an
-   * assertion in ~ComputedStyle.
-   */
-  void ClearArenaRefPtrs(mozilla::ArenaObjectID aObjectID);
-
-  /**
    * Increment nsWindowSizes with sizes of interesting objects allocated in this
    * arena.
    */
   void AddSizeOfExcludingThis(nsWindowSizes& aWindowSizes) const;
 
 #ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
   void Check() {
     mPool.Check();