deleted file mode 100644
--- a/dom/animation/KeyframeEffect.cpp
+++ /dev/null
@@ -1,70 +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/. */
-
-#include "mozilla/dom/KeyframeEffect.h"
-
-#include "mozilla/ComputedStyle.h"
-#include "mozilla/dom/KeyframeAnimationOptionsBinding.h"
-  // For UnrestrictedDoubleOrKeyframeAnimationOptions
-#include "mozilla/dom/AnimationEffectTiming.h"
-#include "mozilla/dom/KeyframeEffectBinding.h"
-#include "nsDocument.h" // For nsDocument::IsWebAnimationsEnabled
-#include "nsDOMMutationObserver.h" // For nsAutoAnimationMutationBatch
-
-namespace mozilla {
-namespace dom {
-
-KeyframeEffect::KeyframeEffect(nsIDocument* aDocument,
-                               const Maybe<OwningAnimationTarget>& aTarget,
-                               const TimingParams& aTiming,
-                               const KeyframeEffectParams& aOptions)
-  : KeyframeEffectReadOnly(aDocument, aTarget,
-                           new AnimationEffectTiming(aDocument, aTiming, this),
-                           aOptions)
-{
-}
-
-JSObject*
-KeyframeEffect::WrapObject(JSContext* aCx,
-                           JS::Handle<JSObject*> aGivenProto)
-{
-  return KeyframeEffectBinding::Wrap(aCx, this, aGivenProto);
-}
-
-/* static */ already_AddRefed<KeyframeEffect>
-KeyframeEffect::Constructor(
-    const GlobalObject& aGlobal,
-    const Nullable<ElementOrCSSPseudoElement>& aTarget,
-    JS::Handle<JSObject*> aKeyframes,
-    const UnrestrictedDoubleOrKeyframeEffectOptions& aOptions,
-    ErrorResult& aRv)
-{
-  return ConstructKeyframeEffect<KeyframeEffect>(aGlobal, aTarget, aKeyframes,
-                                                 aOptions, aRv);
-}
-
-/* static */ already_AddRefed<KeyframeEffect>
-KeyframeEffect::Constructor(const GlobalObject& aGlobal,
-                            KeyframeEffectReadOnly& aSource,
-                            ErrorResult& aRv)
-{
-  return ConstructKeyframeEffect<KeyframeEffect>(aGlobal, aSource, aRv);
-}
-
-/* static */ already_AddRefed<KeyframeEffect>
-KeyframeEffect::Constructor(
-    const GlobalObject& aGlobal,
-    const Nullable<ElementOrCSSPseudoElement>& aTarget,
-    JS::Handle<JSObject*> aKeyframes,
-    const UnrestrictedDoubleOrKeyframeAnimationOptions& aOptions,
-    ErrorResult& aRv)
-{
-  return ConstructKeyframeEffect<KeyframeEffect>(aGlobal, aTarget, aKeyframes,
-                                                 aOptions, aRv);
-}
-
-} // namespace dom
-} // namespace mozilla

deleted file mode 100644
--- a/dom/animation/KeyframeEffect.h
+++ /dev/null
@@ -1,70 +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/. */
-
-#ifndef mozilla_dom_KeyframeEffect_h
-#define mozilla_dom_KeyframeEffect_h
-
-#include "nsWrapperCache.h"
-#include "mozilla/dom/BindingDeclarations.h"
-#include "mozilla/dom/KeyframeEffectReadOnly.h"
-#include "mozilla/AnimationTarget.h" // For (Non)OwningAnimationTarget
-#include "mozilla/Maybe.h"
-
-struct JSContext;
-class JSObject;
-class nsIDocument;
-
-namespace mozilla {
-
-class ErrorResult;
-struct KeyframeEffectParams;
-struct TimingParams;
-
-namespace dom {
-
-class ElementOrCSSPseudoElement;
-class GlobalObject;
-class UnrestrictedDoubleOrKeyframeAnimationOptions;
-class UnrestrictedDoubleOrKeyframeEffectOptions;
-
-class KeyframeEffect : public KeyframeEffectReadOnly
-{
-public:
-  KeyframeEffect(nsIDocument* aDocument,
-                 const Maybe<OwningAnimationTarget>& aTarget,
-                 const TimingParams& aTiming,
-                 const KeyframeEffectParams& aOptions);
-
-  JSObject* WrapObject(JSContext* aCx,
-                       JS::Handle<JSObject*> aGivenProto) override;
-
-  static already_AddRefed<KeyframeEffect>
-  Constructor(const GlobalObject& aGlobal,
-              const Nullable<ElementOrCSSPseudoElement>& aTarget,
-              JS::Handle<JSObject*> aKeyframes,
-              const UnrestrictedDoubleOrKeyframeEffectOptions& aOptions,
-              ErrorResult& aRv);
-
-  static already_AddRefed<KeyframeEffect>
-  Constructor(const GlobalObject& aGlobal,
-              KeyframeEffectReadOnly& aSource,
-              ErrorResult& aRv);
-
-  // Variant of Constructor that accepts a KeyframeAnimationOptions object
-  // for use with for Animatable.animate.
-  // Not exposed to content.
-  static already_AddRefed<KeyframeEffect>
-  Constructor(const GlobalObject& aGlobal,
-              const Nullable<ElementOrCSSPseudoElement>& aTarget,
-              JS::Handle<JSObject*> aKeyframes,
-              const UnrestrictedDoubleOrKeyframeAnimationOptions& aOptions,
-              ErrorResult& aRv);
-};
-
-} // namespace dom
-} // namespace mozilla
-
-#endif // mozilla_dom_KeyframeEffect_h

--- a/dom/animation/KeyframeEffectReadOnly.cpp
+++ b/dom/animation/KeyframeEffectReadOnly.cpp
@@ -1799,11 +1799,59 @@ KeyframeEffectReadOnly::UpdateEffectSet(
   if (HasAnimationOfProperty(eCSSProperty_transform)) {
     effectSet->SetMayHaveTransformAnimation();
     if (frame) {
       frame->SetMayHaveTransformAnimation();
     }
   }
 }
 
+KeyframeEffect::KeyframeEffect(nsIDocument* aDocument,
+                               const Maybe<OwningAnimationTarget>& aTarget,
+                               const TimingParams& aTiming,
+                               const KeyframeEffectParams& aOptions)
+  : KeyframeEffectReadOnly(aDocument, aTarget,
+                           new AnimationEffectTiming(aDocument, aTiming, this),
+                           aOptions)
+{
+}
+
+JSObject*
+KeyframeEffect::WrapObject(JSContext* aCx,
+                           JS::Handle<JSObject*> aGivenProto)
+{
+  return KeyframeEffectBinding::Wrap(aCx, this, aGivenProto);
+}
+
+/* static */ already_AddRefed<KeyframeEffect>
+KeyframeEffect::Constructor(
+    const GlobalObject& aGlobal,
+    const Nullable<ElementOrCSSPseudoElement>& aTarget,
+    JS::Handle<JSObject*> aKeyframes,
+    const UnrestrictedDoubleOrKeyframeEffectOptions& aOptions,
+    ErrorResult& aRv)
+{
+  return ConstructKeyframeEffect<KeyframeEffect>(aGlobal, aTarget, aKeyframes,
+                                                 aOptions, aRv);
+}
+
+/* static */ already_AddRefed<KeyframeEffect>
+KeyframeEffect::Constructor(const GlobalObject& aGlobal,
+                            KeyframeEffectReadOnly& aSource,
+                            ErrorResult& aRv)
+{
+  return ConstructKeyframeEffect<KeyframeEffect>(aGlobal, aSource, aRv);
+}
+
+/* static */ already_AddRefed<KeyframeEffect>
+KeyframeEffect::Constructor(
+    const GlobalObject& aGlobal,
+    const Nullable<ElementOrCSSPseudoElement>& aTarget,
+    JS::Handle<JSObject*> aKeyframes,
+    const UnrestrictedDoubleOrKeyframeAnimationOptions& aOptions,
+    ErrorResult& aRv)
+{
+  return ConstructKeyframeEffect<KeyframeEffect>(aGlobal, aTarget, aKeyframes,
+                                                 aOptions, aRv);
+}
 
 } // namespace dom
 } // namespace mozilla

--- a/dom/animation/KeyframeEffectReadOnly.h
+++ b/dom/animation/KeyframeEffectReadOnly.h
@@ -449,12 +449,46 @@ private:
   // Returns true if this effect causes visibility change.
   // (i.e. 'visibility: hidden' -> 'visibility: visible' and vice versa.)
   bool HasVisibilityChange() const
   {
     return mCumulativeChangeHint & nsChangeHint_VisibilityChange;
   }
 };
 
+class KeyframeEffect : public KeyframeEffectReadOnly
+{
+public:
+  KeyframeEffect(nsIDocument* aDocument,
+                 const Maybe<OwningAnimationTarget>& aTarget,
+                 const TimingParams& aTiming,
+                 const KeyframeEffectParams& aOptions);
+
+  JSObject* WrapObject(JSContext* aCx,
+                       JS::Handle<JSObject*> aGivenProto) override;
+
+  static already_AddRefed<KeyframeEffect>
+  Constructor(const GlobalObject& aGlobal,
+              const Nullable<ElementOrCSSPseudoElement>& aTarget,
+              JS::Handle<JSObject*> aKeyframes,
+              const UnrestrictedDoubleOrKeyframeEffectOptions& aOptions,
+              ErrorResult& aRv);
+
+  static already_AddRefed<KeyframeEffect>
+  Constructor(const GlobalObject& aGlobal,
+              KeyframeEffectReadOnly& aSource,
+              ErrorResult& aRv);
+
+  // Variant of Constructor that accepts a KeyframeAnimationOptions object
+  // for use with for Animatable.animate.
+  // Not exposed to content.
+  static already_AddRefed<KeyframeEffect>
+  Constructor(const GlobalObject& aGlobal,
+              const Nullable<ElementOrCSSPseudoElement>& aTarget,
+              JS::Handle<JSObject*> aKeyframes,
+              const UnrestrictedDoubleOrKeyframeAnimationOptions& aOptions,
+              ErrorResult& aRv);
+};
+
 } // namespace dom
 } // namespace mozilla
 
 #endif // mozilla_dom_KeyframeEffectReadOnly_h

--- a/dom/animation/moz.build
+++ b/dom/animation/moz.build
@@ -13,17 +13,16 @@ MOCHITEST_CHROME_MANIFESTS += ['test/chr
 EXPORTS.mozilla.dom += [
     'Animation.h',
     'AnimationEffectReadOnly.h',
     'AnimationEffectTiming.h',
     'AnimationEffectTimingReadOnly.h',
     'AnimationTimeline.h',
     'CSSPseudoElement.h',
     'DocumentTimeline.h',
-    'KeyframeEffect.h',
     'KeyframeEffectReadOnly.h',
 ]
 
 EXPORTS.mozilla += [
     'AnimationComparator.h',
     'AnimationEventDispatcher.h',
     'AnimationPerformanceWarning.h',
     'AnimationPropertySegment.h',
@@ -50,17 +49,16 @@ UNIFIED_SOURCES += [
     'AnimationPerformanceWarning.cpp',
     'AnimationTimeline.cpp',
     'AnimationUtils.cpp',
     'ComputedTimingFunction.cpp',
     'CSSPseudoElement.cpp',
     'DocumentTimeline.cpp',
     'EffectCompositor.cpp',
     'EffectSet.cpp',
-    'KeyframeEffect.cpp',
     'KeyframeEffectReadOnly.cpp',
     'KeyframeUtils.cpp',
     'PendingAnimationTracker.cpp',
     'TimingParams.cpp',
 ]
 
 LOCAL_INCLUDES += [
     '/dom/base',

--- a/dom/base/Element.cpp
+++ b/dom/base/Element.cpp
@@ -131,18 +131,18 @@
 #include "nsStyledElement.h"
 #include "nsXBLService.h"
 #include "nsITextControlElement.h"
 #include "nsITextControlFrame.h"
 #include "nsISupportsImpl.h"
 #include "mozilla/dom/CSSPseudoElement.h"
 #include "mozilla/dom/DocumentFragment.h"
 #include "mozilla/dom/ElementBinding.h"
-#include "mozilla/dom/KeyframeEffect.h"
 #include "mozilla/dom/KeyframeEffectBinding.h"
+#include "mozilla/dom/KeyframeEffectReadOnly.h"
 #include "mozilla/dom/MouseEventBinding.h"
 #include "mozilla/dom/WindowBinding.h"
 #include "mozilla/dom/VRDisplay.h"
 #include "mozilla/IntegerPrintfMacros.h"
 #include "mozilla/Preferences.h"
 #include "nsComputedDOMStyle.h"
 #include "nsDOMStringMap.h"
 #include "DOMIntersectionObserver.h"

--- a/dom/webidl/KeyframeEffect.webidl
+++ b/dom/webidl/KeyframeEffect.webidl
@@ -57,16 +57,17 @@ dictionary AnimationPropertyDetails {
 partial interface KeyframeEffectReadOnly {
   [ChromeOnly, Throws] sequence<AnimationPropertyDetails> getProperties();
 };
 
 // KeyframeEffect should run in the caller's compartment to do custom
 // processing on the `keyframes` object.
 [Func="nsDocument::IsWebAnimationsEnabled",
  RunConstructorInCallerCompartment,
+ HeaderFile="mozilla/dom/KeyframeEffectReadOnly.h",
  Constructor ((Element or CSSPseudoElement)? target,
               object? keyframes,
               optional (unrestricted double or KeyframeEffectOptions) options),
  Constructor (KeyframeEffectReadOnly source)]
 interface KeyframeEffect : KeyframeEffectReadOnly {
   [Throws]
   void setKeyframes (object? keyframes);
 };