diff --git a/gfx/layers/Layers.cpp b/gfx/layers/Layers.cpp
index 8574afc886d..022a1ed3b1e 100644
--- a/gfx/layers/Layers.cpp
+++ b/gfx/layers/Layers.cpp
@@ -190,6 +190,8 @@ Layer::AddAnimation()
 {
   MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) AddAnimation", this));
 
+  MOZ_ASSERT(!mPendingAnimations, "should have called ClearAnimations first");
+
   Animation* anim = mAnimations.AppendElement();
 
   Mutated();
@@ -199,6 +201,8 @@ Layer::AddAnimation()
 void
 Layer::ClearAnimations()
 {
+  mPendingAnimations = nullptr;
+
   if (mAnimations.IsEmpty() && mAnimationData.IsEmpty()) {
     return;
   }
@@ -209,6 +213,28 @@ Layer::ClearAnimations()
   Mutated();
 }
 
+Animation*
+Layer::AddAnimationForNextTransaction()
+{
+  MOZ_ASSERT(mPendingAnimations,
+             "should have called ClearAnimationsForNextTransaction first");
+
+  Animation* anim = mPendingAnimations->AppendElement();
+
+  return anim;
+}
+
+void
+Layer::ClearAnimationsForNextTransaction()
+{
+  // Ensure we have a non-null mPendingAnimations to mark a future clear.
+  if (!mPendingAnimations) {
+    mPendingAnimations = new AnimationArray;
+  }
+
+  mPendingAnimations->Clear();
+}
+
 static nsCSSValueSharedList*
 CreateCSSValueList(const InfallibleTArray<TransformFunction>& aFunctions)
 {
@@ -641,6 +667,13 @@ Layer::ApplyPendingUpdatesForThisTransaction()
     Mutated();
   }
   mPendingTransform = nullptr;
+
+  if (mPendingAnimations) {
+    MOZ_LAYERS_LOG_IF_SHADOWABLE(this, ("Layer::Mutated(%p) PendingUpdatesForThisTransaction", this));
+    mPendingAnimations->SwapElements(mAnimations);
+    mPendingAnimations = nullptr;
+    Mutated();
+  }
 }
 
 const float
diff --git a/gfx/layers/Layers.h b/gfx/layers/Layers.h
index 679ffef14e9..56f04b6d648 100644
--- a/gfx/layers/Layers.h
+++ b/gfx/layers/Layers.h
@@ -950,6 +950,13 @@ public:
   // layout code.  To add an animation to this layer, use AddAnimation.
   void SetAnimations(const AnimationArray& aAnimations);
 
+  // These are a parallel to AddAnimation and clearAnimations, except
+  // they add pending animations that apply only when the next
+  // transaction is begun.  (See also
+  // SetBaseTransformForNextTransaction.)
+  Animation* AddAnimationForNextTransaction();
+  void ClearAnimationsForNextTransaction();
+
   /**
    * CONSTRUCTION PHASE ONLY
    * If a layer is "fixed position", this determines which point on the layer
@@ -1410,6 +1417,8 @@ protected:
   float mPostYScale;
   gfx::Matrix4x4 mEffectiveTransform;
   AnimationArray mAnimations;
+  // See mPendingTransform above.
+  nsAutoPtr<AnimationArray> mPendingAnimations;
   InfallibleTArray<AnimData> mAnimationData;
   float mOpacity;
   gfx::CompositionOp mMixBlendMode;