--- a/dom/base/nsDOMWindowUtils.cpp
+++ b/dom/base/nsDOMWindowUtils.cpp
@@ -2320,17 +2320,17 @@ nsDOMWindowUtils::GetAsyncPanZoomEnabled
   } else {
     *aResult = gfxPlatform::AsyncPanZoomEnabled();
   }
   return NS_OK;
 }
 
 NS_IMETHODIMP
 nsDOMWindowUtils::SetAsyncScrollOffset(nsIDOMNode* aNode,
-                                       int32_t aX, int32_t aY)
+                                       float aX, float aY)
 {
   nsCOMPtr<Element> element = do_QueryInterface(aNode);
   if (!element) {
     return NS_ERROR_INVALID_ARG;
   }
   FrameMetrics::ViewID viewId;
   if (!nsLayoutUtils::FindIDFor(element, &viewId)) {
     return NS_ERROR_UNEXPECTED;

--- a/dom/interfaces/base/nsIDOMWindowUtils.idl
+++ b/dom/interfaces/base/nsIDOMWindowUtils.idl
@@ -1426,17 +1426,17 @@ interface nsIDOMWindowUtils : nsISupport
    */
   readonly attribute bool asyncPanZoomEnabled;
 
   /**
    * Set async scroll offset on an element. The next composite will render
    * with that offset if async scrolling is enabled, and then the offset
    * will be removed. Only call this while test-controlled refreshes is enabled.
    */
-  void setAsyncScrollOffset(in nsIDOMNode aNode, in int32_t aX, in int32_t aY);
+  void setAsyncScrollOffset(in nsIDOMNode aNode, in float aX, in float aY);
 
   /**
    * Set async zoom value. aRootElement should be the document element of our
    * document. The next composite will render with that zoom added to any
    * existing zoom if async scrolling is enabled, and then the zoom will be
    * removed. Only call this while test-controlled refreshes is enabled.
    */
   void setAsyncZoom(in nsIDOMNode aRootElement, in float aValue);

--- a/gfx/layers/ipc/LayerTransactionParent.cpp
+++ b/gfx/layers/ipc/LayerTransactionParent.cpp
@@ -775,17 +775,17 @@ GetAPZCForViewID(Layer* aLayer, FrameMet
       }
     }
   }
   return nullptr;
 }
 
 bool
 LayerTransactionParent::RecvSetAsyncScrollOffset(const FrameMetrics::ViewID& aScrollID,
-                                                 const int32_t& aX, const int32_t& aY)
+                                                 const float& aX, const float& aY)
 {
   if (mDestroyed || !layer_manager() || layer_manager()->IsDestroyed()) {
     return false;
   }
 
   AsyncPanZoomController* controller = GetAPZCForViewID(mRoot, aScrollID);
   if (!controller) {
     return false;

--- a/gfx/layers/ipc/LayerTransactionParent.h
+++ b/gfx/layers/ipc/LayerTransactionParent.h
@@ -127,17 +127,17 @@ protected:
   virtual bool RecvSetTestSampleTime(const TimeStamp& aTime) override;
   virtual bool RecvLeaveTestMode() override;
   virtual bool RecvGetOpacity(PLayerParent* aParent,
                               float* aOpacity) override;
   virtual bool RecvGetAnimationTransform(PLayerParent* aParent,
                                          MaybeTransform* aTransform)
                                          override;
   virtual bool RecvSetAsyncScrollOffset(const FrameMetrics::ViewID& aId,
-                                        const int32_t& aX, const int32_t& aY) override;
+                                        const float& aX, const float& aY) override;
   virtual bool RecvSetAsyncZoom(const FrameMetrics::ViewID& aId,
                                 const float& aValue) override;
   virtual bool RecvFlushApzRepaints() override;
   virtual bool RecvGetAPZTestData(APZTestData* aOutData) override;
   virtual bool RecvRequestProperty(const nsString& aProperty, float* aValue) override;
   virtual bool RecvSetConfirmedTargetAPZC(const uint64_t& aBlockId,
                                           nsTArray<ScrollableLayerGuid>&& aTargets) override;
 

--- a/gfx/layers/ipc/PLayerTransaction.ipdl
+++ b/gfx/layers/ipc/PLayerTransaction.ipdl
@@ -85,17 +85,17 @@ parent:
   // of the corresponding frame and transform origin and after converting to CSS
   // pixels. If the layer is not transformed by animation, the return value will
   // be void_t.
   sync GetAnimationTransform(PLayer layer) returns (MaybeTransform transform);
 
   // The next time the layer tree is composited, add this async scroll offset in
   // CSS pixels for the given ViewID.
   // Useful for testing rendering of async scrolling.
-  sync SetAsyncScrollOffset(ViewID id, int32_t x, int32_t y);
+  sync SetAsyncScrollOffset(ViewID id, float x, float y);
 
   // The next time the layer tree is composited, include this async zoom in
   // for the given ViewID.
   // Useful for testing rendering of async zooming.
   sync SetAsyncZoom(ViewID id, float zoom);
 
   // Flush any pending APZ repaints to the main thread.
   async FlushApzRepaints();