--- a/dom/animation/AnimationEffectReadOnly.cpp
+++ b/dom/animation/AnimationEffectReadOnly.cpp
@@ -5,17 +5,17 @@
  * You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "mozilla/dom/AnimationEffectReadOnly.h"
 #include "mozilla/dom/AnimationEffectReadOnlyBinding.h"
 
 namespace mozilla {
 namespace dom {
 
-NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE(AnimationEffectReadOnly, mParent)
+NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE(AnimationEffectReadOnly, mDocument)
 
 NS_IMPL_CYCLE_COLLECTING_ADDREF(AnimationEffectReadOnly)
 NS_IMPL_CYCLE_COLLECTING_RELEASE(AnimationEffectReadOnly)
 
 NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(AnimationEffectReadOnly)
   NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
   NS_INTERFACE_MAP_ENTRY(nsISupports)
 NS_INTERFACE_MAP_END

--- a/dom/animation/AnimationEffectReadOnly.h
+++ b/dom/animation/AnimationEffectReadOnly.h
@@ -19,30 +19,30 @@ struct ComputedTimingProperties;
 
 class AnimationEffectReadOnly : public nsISupports,
                                 public nsWrapperCache
 {
 public:
   NS_DECL_CYCLE_COLLECTING_ISUPPORTS
   NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS(AnimationEffectReadOnly)
 
-  explicit AnimationEffectReadOnly(nsISupports* aParent)
-    : mParent(aParent)
+  explicit AnimationEffectReadOnly(nsIDocument* aDocument)
+    : mDocument(aDocument)
   {
   }
 
-  nsISupports* GetParentObject() const { return mParent; }
+  nsISupports* GetParentObject() const { return mDocument; }
 
   virtual already_AddRefed<AnimationEffectTimingReadOnly> Timing() const = 0;
 
   virtual void GetComputedTimingAsDict(ComputedTimingProperties& aRetVal) const = 0;
 
 protected:
   virtual ~AnimationEffectReadOnly() = default;
 
 protected:
-  nsCOMPtr<nsISupports> mParent;
+  RefPtr<nsIDocument> mDocument;
 };
 
 } // namespace dom
 } // namespace mozilla
 
 #endif // mozilla_dom_AnimationEffectReadOnly_h