--- a/dom/animation/KeyframeEffect.cpp
+++ b/dom/animation/KeyframeEffect.cpp
@@ -451,29 +451,23 @@ KeyframesEqualIgnoringComputedOffsets(co
 }
 
 // https://w3c.github.io/web-animations/#dom-keyframeeffect-setkeyframes
 void
 KeyframeEffectReadOnly::SetKeyframes(JSContext* aContext,
                                      JS::Handle<JSObject*> aKeyframes,
                                      ErrorResult& aRv)
 {
-  nsIDocument* doc = AnimationUtils::GetCurrentRealmDocument(aContext);
-  if (!doc) {
-    aRv.Throw(NS_ERROR_FAILURE);
-    return;
-  }
-
   nsTArray<Keyframe> keyframes =
     KeyframeUtils::GetKeyframesFromObject(aContext, mDocument, aKeyframes, aRv);
   if (aRv.Failed()) {
     return;
   }
 
-  RefPtr<nsStyleContext> styleContext = GetTargetStyleContext(doc);
+  RefPtr<nsStyleContext> styleContext = GetTargetStyleContext();
   SetKeyframes(Move(keyframes), styleContext);
 }
 
 void
 KeyframeEffectReadOnly::SetKeyframes(nsTArray<Keyframe>&& aKeyframes,
                                   nsStyleContext* aStyleContext)
 {
   if (KeyframesEqualIgnoringComputedOffsets(aKeyframes, mKeyframes)) {
@@ -939,35 +933,31 @@ KeyframeEffectReadOnly::RequestRestyle(
   if (presContext && mTarget && mAnimation) {
     presContext->EffectCompositor()->
       RequestRestyle(mTarget->mElement, mTarget->mPseudoType,
                      aRestyleType, mAnimation->CascadeLevel());
   }
 }
 
 already_AddRefed<nsStyleContext>
-KeyframeEffectReadOnly::GetTargetStyleContext(nsIDocument* aDoc)
+KeyframeEffectReadOnly::GetTargetStyleContext()
 {
-  if (!mTarget) {
+  nsIPresShell* shell = GetPresShell();
+  if (!shell) {
     return nullptr;
   }
 
-  if (!aDoc) {
-    aDoc = mTarget->mElement->OwnerDoc();
-    if (!aDoc) {
-      return nullptr;
-    }
-  }
+  MOZ_ASSERT(mTarget,
+             "Should only have a presshell when we have a target element");
 
   nsIAtom* pseudo = mTarget->mPseudoType < CSSPseudoElementType::Count
                     ? nsCSSPseudoElements::GetPseudoAtom(mTarget->mPseudoType)
                     : nullptr;
   return nsComputedDOMStyle::GetStyleContextForElement(mTarget->mElement,
-                                                       pseudo,
-                                                       aDoc->GetShell());
+                                                       pseudo, shell);
 }
 
 #ifdef DEBUG
 void
 DumpAnimationProperties(nsTArray<AnimationProperty>& aAnimationProperties)
 {
   for (auto& p : aAnimationProperties) {
     printf("%s\n", nsCSSProps::GetStringValue(p.mProperty).get());

--- a/dom/animation/KeyframeEffect.h
+++ b/dom/animation/KeyframeEffect.h
@@ -395,19 +395,18 @@ protected:
   // have changed, or when the target frame might have changed.
   void MaybeUpdateFrameForCompositor();
 
   // Looks up the style context associated with the target element, if any.
   // We need to be careful to *not* call this when we are updating the style
   // context. That's because calling GetStyleContextForElement when we are in
   // the process of building a style context may trigger various forms of
   // infinite recursion.
-  // If aDoc is nullptr, we will use the owner doc of the target element.
   already_AddRefed<nsStyleContext>
-  GetTargetStyleContext(nsIDocument* aDoc = nullptr);
+  GetTargetStyleContext();
 
   Maybe<OwningAnimationTarget> mTarget;
   RefPtr<Animation> mAnimation;
 
   RefPtr<AnimationEffectTimingReadOnly> mTiming;
   KeyframeEffectParams mEffectOptions;
 
   // The specified keyframes.