diff --git a/dom/ipc/TabParent.cpp b/dom/ipc/TabParent.cpp
index a9730661432..539db60b1c5 100644
--- a/dom/ipc/TabParent.cpp
+++ b/dom/ipc/TabParent.cpp
@@ -995,7 +995,7 @@ TabParent::AcknowledgeScrollUpdate(const ViewID& aScrollId, const uint32_t& aScr
 }
 
 void TabParent::HandleDoubleTap(const CSSPoint& aPoint,
-                                int32_t aModifiers,
+                                Modifiers aModifiers,
                                 const ScrollableLayerGuid &aGuid)
 {
   if (!mIsDestroyed) {
@@ -1004,7 +1004,7 @@ void TabParent::HandleDoubleTap(const CSSPoint& aPoint,
 }
 
 void TabParent::HandleSingleTap(const CSSPoint& aPoint,
-                                int32_t aModifiers,
+                                Modifiers aModifiers,
                                 const ScrollableLayerGuid &aGuid)
 {
   // TODO Send the modifier data to TabChild for use in mouse events.
@@ -1014,7 +1014,7 @@ void TabParent::HandleSingleTap(const CSSPoint& aPoint,
 }
 
 void TabParent::HandleLongTap(const CSSPoint& aPoint,
-                              int32_t aModifiers,
+                              Modifiers aModifiers,
                               const ScrollableLayerGuid &aGuid,
                               uint64_t aInputBlockId)
 {
@@ -1024,7 +1024,7 @@ void TabParent::HandleLongTap(const CSSPoint& aPoint,
 }
 
 void TabParent::HandleLongTapUp(const CSSPoint& aPoint,
-                                int32_t aModifiers,
+                                Modifiers aModifiers,
                                 const ScrollableLayerGuid &aGuid)
 {
   if (!mIsDestroyed) {
diff --git a/dom/ipc/TabParent.h b/dom/ipc/TabParent.h
index 461dde7a5d4..c23e67e3189 100644
--- a/dom/ipc/TabParent.h
+++ b/dom/ipc/TabParent.h
@@ -251,17 +251,17 @@ public:
     void UIResolutionChanged();
     void AcknowledgeScrollUpdate(const ViewID& aScrollId, const uint32_t& aScrollGeneration);
     void HandleDoubleTap(const CSSPoint& aPoint,
-                         int32_t aModifiers,
+                         Modifiers aModifiers,
                          const ScrollableLayerGuid& aGuid);
     void HandleSingleTap(const CSSPoint& aPoint,
-                         int32_t aModifiers,
+                         Modifiers aModifiers,
                          const ScrollableLayerGuid& aGuid);
     void HandleLongTap(const CSSPoint& aPoint,
-                       int32_t aModifiers,
+                       Modifiers aModifiers,
                        const ScrollableLayerGuid& aGuid,
                        uint64_t aInputBlockId);
     void HandleLongTapUp(const CSSPoint& aPoint,
-                         int32_t aModifiers,
+                         Modifiers aModifiers,
                          const ScrollableLayerGuid& aGuid);
     void NotifyAPZStateChange(ViewID aViewId,
                               APZStateChange aChange,
diff --git a/gfx/layers/apz/public/GeckoContentController.h b/gfx/layers/apz/public/GeckoContentController.h
index c7bf03ea8bd..c479236e766 100644
--- a/gfx/layers/apz/public/GeckoContentController.h
+++ b/gfx/layers/apz/public/GeckoContentController.h
@@ -10,6 +10,7 @@
 #include "FrameMetrics.h"               // for FrameMetrics, etc
 #include "Units.h"                      // for CSSPoint, CSSRect, etc
 #include "mozilla/Assertions.h"         // for MOZ_ASSERT_HELPER2
+#include "mozilla/EventForwards.h"      // for Modifiers
 #include "nsISupportsImpl.h"
 
 class Task;
@@ -44,7 +45,7 @@ public:
    * to.
    */
   virtual void HandleDoubleTap(const CSSPoint& aPoint,
-                               int32_t aModifiers,
+                               Modifiers aModifiers,
                                const ScrollableLayerGuid& aGuid) = 0;
 
   /**
@@ -53,7 +54,7 @@ public:
    * button down, then mouse button up at |aPoint|.
    */
   virtual void HandleSingleTap(const CSSPoint& aPoint,
-                               int32_t aModifiers,
+                               Modifiers aModifiers,
                                const ScrollableLayerGuid& aGuid) = 0;
 
   /**
@@ -61,7 +62,7 @@ public:
    * current scroll offset.
    */
   virtual void HandleLongTap(const CSSPoint& aPoint,
-                             int32_t aModifiers,
+                             Modifiers aModifiers,
                              const ScrollableLayerGuid& aGuid,
                              uint64_t aInputBlockId) = 0;
 
@@ -74,7 +75,7 @@ public:
    * notifies the APZ that the long-tap event was prevent-defaulted).
    */
   virtual void HandleLongTapUp(const CSSPoint& aPoint,
-                               int32_t aModifiers,
+                               Modifiers aModifiers,
                                const ScrollableLayerGuid& aGuid) = 0;
 
   /**
diff --git a/gfx/layers/apz/src/AsyncPanZoomController.cpp b/gfx/layers/apz/src/AsyncPanZoomController.cpp
index d7ca82c0465..d78b636d11e 100644
--- a/gfx/layers/apz/src/AsyncPanZoomController.cpp
+++ b/gfx/layers/apz/src/AsyncPanZoomController.cpp
@@ -84,57 +84,6 @@
 #  define APZC_LOG_FM(fm, prefix, ...)
 #endif
 
-// Static helper functions
-namespace {
-
-int32_t
-WidgetModifiersToDOMModifiers(mozilla::Modifiers aModifiers)
-{
-  int32_t result = 0;
-  if (aModifiers & mozilla::MODIFIER_SHIFT) {
-    result |= nsIDOMWindowUtils::MODIFIER_SHIFT;
-  }
-  if (aModifiers & mozilla::MODIFIER_CONTROL) {
-    result |= nsIDOMWindowUtils::MODIFIER_CONTROL;
-  }
-  if (aModifiers & mozilla::MODIFIER_ALT) {
-    result |= nsIDOMWindowUtils::MODIFIER_ALT;
-  }
-  if (aModifiers & mozilla::MODIFIER_META) {
-    result |= nsIDOMWindowUtils::MODIFIER_META;
-  }
-  if (aModifiers & mozilla::MODIFIER_ALTGRAPH) {
-    result |= nsIDOMWindowUtils::MODIFIER_ALTGRAPH;
-  }
-  if (aModifiers & mozilla::MODIFIER_CAPSLOCK) {
-    result |= nsIDOMWindowUtils::MODIFIER_CAPSLOCK;
-  }
-  if (aModifiers & mozilla::MODIFIER_FN) {
-    result |= nsIDOMWindowUtils::MODIFIER_FN;
-  }
-  if (aModifiers & mozilla::MODIFIER_FNLOCK) {
-    result |= nsIDOMWindowUtils::MODIFIER_FNLOCK;
-  }
-  if (aModifiers & mozilla::MODIFIER_NUMLOCK) {
-    result |= nsIDOMWindowUtils::MODIFIER_NUMLOCK;
-  }
-  if (aModifiers & mozilla::MODIFIER_SCROLLLOCK) {
-    result |= nsIDOMWindowUtils::MODIFIER_SCROLLLOCK;
-  }
-  if (aModifiers & mozilla::MODIFIER_SYMBOL) {
-    result |= nsIDOMWindowUtils::MODIFIER_SYMBOL;
-  }
-  if (aModifiers & mozilla::MODIFIER_SYMBOLLOCK) {
-    result |= nsIDOMWindowUtils::MODIFIER_SYMBOLLOCK;
-  }
-  if (aModifiers & mozilla::MODIFIER_OS) {
-    result |= nsIDOMWindowUtils::MODIFIER_OS;
-  }
-  return result;
-}
-
-}
-
 namespace mozilla {
 namespace layers {
 
@@ -1653,7 +1602,6 @@ nsEventStatus AsyncPanZoomController::OnLongPress(const TapGestureInput& aEvent)
   APZC_LOG("%p got a long-press in state %d\n", this, mState);
   nsRefPtr<GeckoContentController> controller = GetGeckoContentController();
   if (controller) {
-    int32_t modifiers = WidgetModifiersToDOMModifiers(aEvent.modifiers);
     CSSPoint geckoScreenPoint;
     if (ConvertToGecko(aEvent.mLocalPoint, &geckoScreenPoint)) {
       if (CurrentTouchBlock()->IsDuringFastMotion()) {
@@ -1661,7 +1609,7 @@ nsEventStatus AsyncPanZoomController::OnLongPress(const TapGestureInput& aEvent)
         return nsEventStatus_eIgnore;
       }
       uint64_t blockId = GetInputQueue()->InjectNewTouchBlock(this);
-      controller->HandleLongTap(geckoScreenPoint, modifiers, GetGuid(), blockId);
+      controller->HandleLongTap(geckoScreenPoint, aEvent.modifiers, GetGuid(), blockId);
       return nsEventStatus_eConsumeNoDefault;
     }
   }
@@ -1672,10 +1620,9 @@ nsEventStatus AsyncPanZoomController::OnLongPressUp(const TapGestureInput& aEven
   APZC_LOG("%p got a long-tap-up in state %d\n", this, mState);
   nsRefPtr<GeckoContentController> controller = GetGeckoContentController();
   if (controller) {
-    int32_t modifiers = WidgetModifiersToDOMModifiers(aEvent.modifiers);
     CSSPoint geckoScreenPoint;
     if (ConvertToGecko(aEvent.mLocalPoint, &geckoScreenPoint)) {
-      controller->HandleLongTapUp(geckoScreenPoint, modifiers, GetGuid());
+      controller->HandleLongTapUp(geckoScreenPoint, aEvent.modifiers, GetGuid());
       return nsEventStatus_eConsumeNoDefault;
     }
   }
@@ -1697,7 +1644,7 @@ nsEventStatus AsyncPanZoomController::GenerateSingleTap(const ParentLayerPoint&
       // See bug 965381 for the issue this was causing.
       controller->PostDelayedTask(
         NewRunnableMethod(controller.get(), &GeckoContentController::HandleSingleTap,
-                          geckoScreenPoint, WidgetModifiersToDOMModifiers(aModifiers),
+                          geckoScreenPoint, aModifiers,
                           GetGuid()),
         0);
       return nsEventStatus_eConsumeNoDefault;
@@ -1733,10 +1680,9 @@ nsEventStatus AsyncPanZoomController::OnDoubleTap(const TapGestureInput& aEvent)
   nsRefPtr<GeckoContentController> controller = GetGeckoContentController();
   if (controller) {
     if (mZoomConstraints.mAllowDoubleTapZoom && CurrentTouchBlock()->TouchActionAllowsDoubleTapZoom()) {
-      int32_t modifiers = WidgetModifiersToDOMModifiers(aEvent.modifiers);
       CSSPoint geckoScreenPoint;
       if (ConvertToGecko(aEvent.mLocalPoint, &geckoScreenPoint)) {
-        controller->HandleDoubleTap(geckoScreenPoint, modifiers, GetGuid());
+        controller->HandleDoubleTap(geckoScreenPoint, aEvent.modifiers, GetGuid());
       }
     }
     return nsEventStatus_eConsumeNoDefault;
diff --git a/gfx/layers/apz/util/ChromeProcessController.cpp b/gfx/layers/apz/util/ChromeProcessController.cpp
index 3c33bc3eb7a..57c0839c6a9 100644
--- a/gfx/layers/apz/util/ChromeProcessController.cpp
+++ b/gfx/layers/apz/util/ChromeProcessController.cpp
@@ -129,7 +129,7 @@ ChromeProcessController::GetDOMWindowUtils() const
 
 void
 ChromeProcessController::HandleSingleTap(const CSSPoint& aPoint,
-                                         int32_t aModifiers,
+                                         Modifiers aModifiers,
                                          const ScrollableLayerGuid& aGuid)
 {
   if (MessageLoop::current() != mUILoop) {
@@ -144,7 +144,7 @@ ChromeProcessController::HandleSingleTap(const CSSPoint& aPoint,
 }
 
 void
-ChromeProcessController::HandleLongTap(const mozilla::CSSPoint& aPoint, int32_t aModifiers,
+ChromeProcessController::HandleLongTap(const mozilla::CSSPoint& aPoint, Modifiers aModifiers,
                                        const ScrollableLayerGuid& aGuid,
                                        uint64_t aInputBlockId)
 {
@@ -161,7 +161,7 @@ ChromeProcessController::HandleLongTap(const mozilla::CSSPoint& aPoint, int32_t
 }
 
 void
-ChromeProcessController::HandleLongTapUp(const CSSPoint& aPoint, int32_t aModifiers,
+ChromeProcessController::HandleLongTapUp(const CSSPoint& aPoint, Modifiers aModifiers,
                                          const ScrollableLayerGuid& aGuid)
 {
   if (MessageLoop::current() != mUILoop) {
diff --git a/gfx/layers/apz/util/ChromeProcessController.h b/gfx/layers/apz/util/ChromeProcessController.h
index ee91ec6506e..0fc8ec5bfd9 100644
--- a/gfx/layers/apz/util/ChromeProcessController.h
+++ b/gfx/layers/apz/util/ChromeProcessController.h
@@ -40,14 +40,14 @@ public:
   virtual void AcknowledgeScrollUpdate(const FrameMetrics::ViewID& aScrollId,
                                        const uint32_t& aScrollGeneration) MOZ_OVERRIDE;
 
-  virtual void HandleDoubleTap(const mozilla::CSSPoint& aPoint, int32_t aModifiers,
+  virtual void HandleDoubleTap(const mozilla::CSSPoint& aPoint, Modifiers aModifiers,
                                const ScrollableLayerGuid& aGuid) MOZ_OVERRIDE {}
-  virtual void HandleSingleTap(const mozilla::CSSPoint& aPoint, int32_t aModifiers,
+  virtual void HandleSingleTap(const mozilla::CSSPoint& aPoint, Modifiers aModifiers,
                                const ScrollableLayerGuid& aGuid) MOZ_OVERRIDE;
-  virtual void HandleLongTap(const mozilla::CSSPoint& aPoint, int32_t aModifiers,
+  virtual void HandleLongTap(const mozilla::CSSPoint& aPoint, Modifiers aModifiers,
                                const ScrollableLayerGuid& aGuid,
                                uint64_t aInputBlockId) MOZ_OVERRIDE;
-  virtual void HandleLongTapUp(const CSSPoint& aPoint, int32_t aModifiers,
+  virtual void HandleLongTapUp(const CSSPoint& aPoint, Modifiers aModifiers,
                                const ScrollableLayerGuid& aGuid) MOZ_OVERRIDE;
   virtual void SendAsyncScrollDOMEvent(bool aIsRoot, const mozilla::CSSRect &aContentRect,
                                        const mozilla::CSSSize &aScrollableSize) MOZ_OVERRIDE {}
diff --git a/gfx/tests/gtest/TestAsyncPanZoomController.cpp b/gfx/tests/gtest/TestAsyncPanZoomController.cpp
index 7a75f3b7c4d..776e33c874d 100644
--- a/gfx/tests/gtest/TestAsyncPanZoomController.cpp
+++ b/gfx/tests/gtest/TestAsyncPanZoomController.cpp
@@ -62,10 +62,10 @@ class MockContentController : public GeckoContentController {
 public:
   MOCK_METHOD1(RequestContentRepaint, void(const FrameMetrics&));
   MOCK_METHOD2(AcknowledgeScrollUpdate, void(const FrameMetrics::ViewID&, const uint32_t& aScrollGeneration));
-  MOCK_METHOD3(HandleDoubleTap, void(const CSSPoint&, int32_t, const ScrollableLayerGuid&));
-  MOCK_METHOD3(HandleSingleTap, void(const CSSPoint&, int32_t, const ScrollableLayerGuid&));
-  MOCK_METHOD4(HandleLongTap, void(const CSSPoint&, int32_t, const ScrollableLayerGuid&, uint64_t));
-  MOCK_METHOD3(HandleLongTapUp, void(const CSSPoint&, int32_t, const ScrollableLayerGuid&));
+  MOCK_METHOD3(HandleDoubleTap, void(const CSSPoint&, Modifiers, const ScrollableLayerGuid&));
+  MOCK_METHOD3(HandleSingleTap, void(const CSSPoint&, Modifiers, const ScrollableLayerGuid&));
+  MOCK_METHOD4(HandleLongTap, void(const CSSPoint&, Modifiers, const ScrollableLayerGuid&, uint64_t));
+  MOCK_METHOD3(HandleLongTapUp, void(const CSSPoint&, Modifiers, const ScrollableLayerGuid&));
   MOCK_METHOD3(SendAsyncScrollDOMEvent, void(bool aIsRoot, const CSSRect &aContentRect, const CSSSize &aScrollableSize));
   MOCK_METHOD2(PostDelayedTask, void(Task* aTask, int aDelayMs));
   MOCK_METHOD3(NotifyAPZStateChange, void(const ScrollableLayerGuid& aGuid, APZStateChange aChange, int aArg));
diff --git a/layout/ipc/RenderFrameParent.cpp b/layout/ipc/RenderFrameParent.cpp
index 22cfc651735..d0d97b6310c 100644
--- a/layout/ipc/RenderFrameParent.cpp
+++ b/layout/ipc/RenderFrameParent.cpp
@@ -13,6 +13,7 @@
 # include "LayerManagerD3D9.h"
 #endif //MOZ_ENABLE_D3D9_LAYER
 #include "mozilla/BrowserElementParent.h"
+#include "mozilla/EventForwards.h"  // for Modifiers
 #include "mozilla/dom/ContentChild.h"
 #include "mozilla/dom/TabParent.h"
 #include "mozilla/layers/APZCTreeManager.h"
@@ -119,7 +120,7 @@ public:
   }
 
   virtual void HandleDoubleTap(const CSSPoint& aPoint,
-                               int32_t aModifiers,
+                               Modifiers aModifiers,
                                const ScrollableLayerGuid& aGuid) MOZ_OVERRIDE
   {
     if (MessageLoop::current() != mUILoop) {
@@ -138,7 +139,7 @@ public:
   }
 
   virtual void HandleSingleTap(const CSSPoint& aPoint,
-                               int32_t aModifiers,
+                               Modifiers aModifiers,
                                const ScrollableLayerGuid& aGuid) MOZ_OVERRIDE
   {
     if (MessageLoop::current() != mUILoop) {
@@ -158,7 +159,7 @@ public:
   }
 
   virtual void HandleLongTap(const CSSPoint& aPoint,
-                             int32_t aModifiers,
+                             Modifiers aModifiers,
                              const ScrollableLayerGuid& aGuid,
                              uint64_t aInputBlockId) MOZ_OVERRIDE
   {
@@ -178,7 +179,7 @@ public:
   }
 
   virtual void HandleLongTapUp(const CSSPoint& aPoint,
-                               int32_t aModifiers,
+                               Modifiers aModifiers,
                                const ScrollableLayerGuid& aGuid) MOZ_OVERRIDE
   {
     if (MessageLoop::current() != mUILoop) {
diff --git a/widget/android/APZCCallbackHandler.cpp b/widget/android/APZCCallbackHandler.cpp
index 8c4b52ef8f8..66823aa91c3 100644
--- a/widget/android/APZCCallbackHandler.cpp
+++ b/widget/android/APZCCallbackHandler.cpp
@@ -111,7 +111,7 @@ APZCCallbackHandler::AcknowledgeScrollUpdate(const FrameMetrics::ViewID& aScroll
 
 void
 APZCCallbackHandler::HandleDoubleTap(const CSSPoint& aPoint,
-                                     int32_t aModifiers,
+                                     Modifiers aModifiers,
                                      const mozilla::layers::ScrollableLayerGuid& aGuid)
 {
     CSSIntPoint point = RoundedToInt(aPoint);
@@ -122,7 +122,7 @@ APZCCallbackHandler::HandleDoubleTap(const CSSPoint& aPoint,
 
 void
 APZCCallbackHandler::HandleSingleTap(const CSSPoint& aPoint,
-                                     int32_t aModifiers,
+                                     Modifiers aModifiers,
                                      const mozilla::layers::ScrollableLayerGuid& aGuid)
 {
     // FIXME Send the modifier data to Gecko for use in mouse events.
@@ -134,7 +134,7 @@ APZCCallbackHandler::HandleSingleTap(const CSSPoint& aPoint,
 
 void
 APZCCallbackHandler::HandleLongTap(const CSSPoint& aPoint,
-                                   int32_t aModifiers,
+                                   Modifiers aModifiers,
                                    const mozilla::layers::ScrollableLayerGuid& aGuid,
                                    uint64_t aInputBlockId)
 {
@@ -147,7 +147,7 @@ APZCCallbackHandler::HandleLongTap(const CSSPoint& aPoint,
 
 void
 APZCCallbackHandler::HandleLongTapUp(const CSSPoint& aPoint,
-                                     int32_t aModifiers,
+                                     Modifiers aModifiers,
                                      const mozilla::layers::ScrollableLayerGuid& aGuid)
 {
     HandleSingleTap(aPoint, aModifiers, aGuid);
diff --git a/widget/android/APZCCallbackHandler.h b/widget/android/APZCCallbackHandler.h
index df5ccff4954..0aa1f98a30b 100644
--- a/widget/android/APZCCallbackHandler.h
+++ b/widget/android/APZCCallbackHandler.h
@@ -7,6 +7,7 @@
 #define APZCCallbackHandler_h__
 
 #include "mozilla/layers/GeckoContentController.h"
+#include "mozilla/EventForwards.h"  // for Modifiers
 #include "mozilla/StaticPtr.h"
 #include "mozilla/TimeStamp.h"
 #include "GeneratedJNIWrappers.h"
@@ -45,14 +46,14 @@ public: // GeckoContentController methods
     void RequestContentRepaint(const mozilla::layers::FrameMetrics& aFrameMetrics) MOZ_OVERRIDE;
     void AcknowledgeScrollUpdate(const mozilla::layers::FrameMetrics::ViewID& aScrollId,
                                  const uint32_t& aScrollGeneration) MOZ_OVERRIDE;
-    void HandleDoubleTap(const mozilla::CSSPoint& aPoint, int32_t aModifiers,
+    void HandleDoubleTap(const mozilla::CSSPoint& aPoint, Modifiers aModifiers,
                          const mozilla::layers::ScrollableLayerGuid& aGuid) MOZ_OVERRIDE;
-    void HandleSingleTap(const mozilla::CSSPoint& aPoint, int32_t aModifiers,
+    void HandleSingleTap(const mozilla::CSSPoint& aPoint, Modifiers aModifiers,
                          const mozilla::layers::ScrollableLayerGuid& aGuid) MOZ_OVERRIDE;
-    void HandleLongTap(const mozilla::CSSPoint& aPoint, int32_t aModifiers,
+    void HandleLongTap(const mozilla::CSSPoint& aPoint, Modifiers aModifiers,
                        const mozilla::layers::ScrollableLayerGuid& aGuid,
                        uint64_t aInputBlockId) MOZ_OVERRIDE;
-    void HandleLongTapUp(const mozilla::CSSPoint& aPoint, int32_t aModifiers,
+    void HandleLongTapUp(const mozilla::CSSPoint& aPoint, Modifiers aModifiers,
                          const mozilla::layers::ScrollableLayerGuid& aGuid) MOZ_OVERRIDE;
     void SendAsyncScrollDOMEvent(bool aIsRoot, const mozilla::CSSRect& aContentRect,
                                  const mozilla::CSSSize& aScrollableSize) MOZ_OVERRIDE;
diff --git a/widget/windows/winrt/APZController.cpp b/widget/windows/winrt/APZController.cpp
index fff957127c6..3b7c1a2c22f 100644
--- a/widget/windows/winrt/APZController.cpp
+++ b/widget/windows/winrt/APZController.cpp
@@ -200,21 +200,21 @@ APZController::AcknowledgeScrollUpdate(const FrameMetrics::ViewID& aScrollId,
 
 void
 APZController::HandleDoubleTap(const CSSPoint& aPoint,
-                               int32_t aModifiers,
+                               Modifiers aModifiers,
                                const ScrollableLayerGuid& aGuid)
 {
 }
 
 void
 APZController::HandleSingleTap(const CSSPoint& aPoint,
-                               int32_t aModifiers,
+                               Modifiers aModifiers,
                                const ScrollableLayerGuid& aGuid)
 {
 }
 
 void
 APZController::HandleLongTap(const CSSPoint& aPoint,
-                             int32_t aModifiers,
+                             Modifiers aModifiers,
                              const mozilla::layers::ScrollableLayerGuid& aGuid,
                              uint64_t aInputBlockId)
 {
@@ -226,7 +226,7 @@ APZController::HandleLongTap(const CSSPoint& aPoint,
 
 void
 APZController::HandleLongTapUp(const CSSPoint& aPoint,
-                               int32_t aModifiers,
+                               Modifiers aModifiers,
                                const ScrollableLayerGuid& aGuid)
 {
 }
diff --git a/widget/windows/winrt/APZController.h b/widget/windows/winrt/APZController.h
index 3d1cbe24b54..93d4f9d5f7e 100644
--- a/widget/windows/winrt/APZController.h
+++ b/widget/windows/winrt/APZController.h
@@ -39,17 +39,17 @@ public:
   virtual void RequestContentRepaint(const FrameMetrics& aFrameMetrics);
   virtual void AcknowledgeScrollUpdate(const FrameMetrics::ViewID& aScrollId, const uint32_t& aScrollGeneration);
   virtual void HandleDoubleTap(const mozilla::CSSPoint& aPoint,
-                               int32_t aModifiers,
+                               Modifiers aModifiers,
                                const mozilla::layers::ScrollableLayerGuid& aGuid);
   virtual void HandleSingleTap(const mozilla::CSSPoint& aPoint,
-                               int32_t aModifiers,
+                               Modifiers aModifiers,
                                const mozilla::layers::ScrollableLayerGuid& aGuid);
   virtual void HandleLongTap(const mozilla::CSSPoint& aPoint,
-                             int32_t aModifiers,
+                             Modifiers aModifiers,
                              const mozilla::layers::ScrollableLayerGuid& aGuid,
                              uint64_t aInputBlockId);
   virtual void HandleLongTapUp(const mozilla::CSSPoint& aPoint,
-                               int32_t aModifiers,
+                               Modifiers aModifiers,
                                const mozilla::layers::ScrollableLayerGuid& aGuid);
   virtual void SendAsyncScrollDOMEvent(bool aIsRoot, const mozilla::CSSRect &aContentRect, const mozilla::CSSSize &aScrollableSize);
   virtual void PostDelayedTask(Task* aTask, int aDelayMs);