diff --git a/content/events/src/nsDOMEvent.cpp b/content/events/src/nsDOMEvent.cpp
index ccd433993777..e559c982e78f 100644
--- a/content/events/src/nsDOMEvent.cpp
+++ b/content/events/src/nsDOMEvent.cpp
@@ -605,10 +605,10 @@ nsDOMEvent::DuplicatePrivateData()
     }
     case NS_MOUSE_SCROLL_EVENT:
     {
-      nsMouseScrollEvent* oldMouseScrollEvent =
-        static_cast<nsMouseScrollEvent*>(mEvent);
-      nsMouseScrollEvent* mouseScrollEvent =
-        new nsMouseScrollEvent(false, msg, nullptr);
+      WidgetMouseScrollEvent* oldMouseScrollEvent =
+        static_cast<WidgetMouseScrollEvent*>(mEvent);
+      WidgetMouseScrollEvent* mouseScrollEvent =
+        new WidgetMouseScrollEvent(false, msg, nullptr);
       mouseScrollEvent->AssignMouseScrollEventData(*oldMouseScrollEvent, true);
       newEvent = mouseScrollEvent;
       break;
diff --git a/content/events/src/nsDOMMouseEvent.cpp b/content/events/src/nsDOMMouseEvent.cpp
index e3d95b385704..33f2cf1a495a 100644
--- a/content/events/src/nsDOMMouseEvent.cpp
+++ b/content/events/src/nsDOMMouseEvent.cpp
@@ -18,7 +18,7 @@ nsDOMMouseEvent::nsDOMMouseEvent(mozilla::dom::EventTarget* aOwner,
                  new nsMouseEvent(false, 0, nullptr,
                                   nsMouseEvent::eReal))
 {
-  // There's no way to make this class' ctor allocate an nsMouseScrollEvent.
+  // There's no way to make this class' ctor allocate an WidgetMouseScrollEvent.
   // It's not that important, though, since a scroll event is not a real
   // DOM event.
   
diff --git a/content/events/src/nsDOMMouseScrollEvent.cpp b/content/events/src/nsDOMMouseScrollEvent.cpp
index fbcfba846e69..bcf6445b92cf 100644
--- a/content/events/src/nsDOMMouseScrollEvent.cpp
+++ b/content/events/src/nsDOMMouseScrollEvent.cpp
@@ -13,7 +13,8 @@ nsDOMMouseScrollEvent::nsDOMMouseScrollEvent(mozilla::dom::EventTarget* aOwner,
                                              nsPresContext* aPresContext,
                                              WidgetInputEvent* aEvent)
   : nsDOMMouseEvent(aOwner, aPresContext,
-                    aEvent ? aEvent : new nsMouseScrollEvent(false, 0, nullptr))
+                    aEvent ? aEvent :
+                             new WidgetMouseScrollEvent(false, 0, nullptr))
 {
   if (aEvent) {
     mEventIsInternal = false;
@@ -25,7 +26,7 @@ nsDOMMouseScrollEvent::nsDOMMouseScrollEvent(mozilla::dom::EventTarget* aOwner,
   }
 
   if(mEvent->eventStructType == NS_MOUSE_SCROLL_EVENT) {
-    mDetail = static_cast<nsMouseScrollEvent*>(mEvent)->delta;
+    mDetail = static_cast<WidgetMouseScrollEvent*>(mEvent)->delta;
   }
 }
 
@@ -35,7 +36,7 @@ nsDOMMouseScrollEvent::~nsDOMMouseScrollEvent()
     switch (mEvent->eventStructType)
     {
       case NS_MOUSE_SCROLL_EVENT:
-        delete static_cast<nsMouseScrollEvent*>(mEvent);
+        delete static_cast<WidgetMouseScrollEvent*>(mEvent);
         break;
       default:
         delete mEvent;
@@ -66,7 +67,7 @@ nsDOMMouseScrollEvent::InitMouseScrollEvent(const nsAString & aType, bool aCanBu
   NS_ENSURE_SUCCESS(rv, rv);
   
   if (mEvent->eventStructType == NS_MOUSE_SCROLL_EVENT) {
-    static_cast<nsMouseScrollEvent*>(mEvent)->isHorizontal =
+    static_cast<WidgetMouseScrollEvent*>(mEvent)->isHorizontal =
                                                 (aAxis == HORIZONTAL_AXIS);
   }
 
@@ -86,7 +87,7 @@ int32_t
 nsDOMMouseScrollEvent::Axis()
 {
   if (mEvent->eventStructType == NS_MOUSE_SCROLL_EVENT) {
-    return static_cast<nsMouseScrollEvent*>(mEvent)->isHorizontal ?
+    return static_cast<WidgetMouseScrollEvent*>(mEvent)->isHorizontal ?
              static_cast<int32_t>(HORIZONTAL_AXIS) :
              static_cast<int32_t>(VERTICAL_AXIS);
   }
diff --git a/content/events/src/nsEventStateManager.cpp b/content/events/src/nsEventStateManager.cpp
index 51f363960f3f..8face3cbeaed 100644
--- a/content/events/src/nsEventStateManager.cpp
+++ b/content/events/src/nsEventStateManager.cpp
@@ -2478,8 +2478,8 @@ nsEventStateManager::SendLineScrollEvent(nsIFrame* aTargetFrame,
     targetContent = targetContent->GetParent();
   }
 
-  nsMouseScrollEvent event(aEvent->mFlags.mIsTrusted, NS_MOUSE_SCROLL,
-                           aEvent->widget);
+  WidgetMouseScrollEvent event(aEvent->mFlags.mIsTrusted, NS_MOUSE_SCROLL,
+                               aEvent->widget);
   if (*aStatus == nsEventStatus_eConsumeNoDefault) {
     event.mFlags.mDefaultPrevented = true;
   }
@@ -2514,8 +2514,8 @@ nsEventStateManager::SendPixelScrollEvent(nsIFrame* aTargetFrame,
     targetContent = targetContent->GetParent();
   }
 
-  nsMouseScrollEvent event(aEvent->mFlags.mIsTrusted, NS_MOUSE_PIXEL_SCROLL,
-                           aEvent->widget);
+  WidgetMouseScrollEvent event(aEvent->mFlags.mIsTrusted, NS_MOUSE_PIXEL_SCROLL,
+                               aEvent->widget);
   if (*aStatus == nsEventStatus_eConsumeNoDefault) {
     event.mFlags.mDefaultPrevented = true;
   }
diff --git a/dom/ipc/PBrowser.ipdl b/dom/ipc/PBrowser.ipdl
index 5fd7af928009..d20fa671a7e8 100644
--- a/dom/ipc/PBrowser.ipdl
+++ b/dom/ipc/PBrowser.ipdl
@@ -43,7 +43,6 @@ using nsIntRect;
 using nsIntSize;
 using mozilla::WidgetKeyboardEvent;
 using nsMouseEvent;
-using nsMouseScrollEvent;
 using mozilla::WheelEvent;
 using nsRect;
 using mozilla::WidgetSelectionEvent;
diff --git a/widget/EventForwards.h b/widget/EventForwards.h
index db60b1197aa5..f217fbef737f 100644
--- a/widget/EventForwards.h
+++ b/widget/EventForwards.h
@@ -106,7 +106,6 @@ class InternalMutationEvent;
 typedef mozilla::WidgetEvent               nsEvent;
 typedef mozilla::WidgetGUIEvent            nsGUIEvent;
 typedef mozilla::WidgetMouseEvent          nsMouseEvent;
-typedef mozilla::WidgetMouseScrollEvent    nsMouseScrollEvent;
 
 namespace mozilla {
 typedef WidgetWheelEvent                   WheelEvent;
diff --git a/widget/MouseEvents.h b/widget/MouseEvents.h
index 1373027da5d5..a604f0a0da11 100644
--- a/widget/MouseEvents.h
+++ b/widget/MouseEvents.h
@@ -425,6 +425,5 @@ typedef WidgetWheelEvent                WheelEvent;
 
 // TODO: Remove following typedefs
 typedef mozilla::WidgetMouseEvent       nsMouseEvent;
-typedef mozilla::WidgetMouseScrollEvent nsMouseScrollEvent;
 
 #endif // mozilla_MouseEvents_h__
diff --git a/widget/cocoa/nsChildView.mm b/widget/cocoa/nsChildView.mm
index 69bad8854a2e..7718b045c1c5 100644
--- a/widget/cocoa/nsChildView.mm
+++ b/widget/cocoa/nsChildView.mm
@@ -4122,9 +4122,9 @@ NSEvent* gLastDragMouseDownEvent = nil;
 
   // Only initiate tracking if the user has tried to scroll past the edge of
   // the current page (as indicated by 'overflow' being non-zero).  Gecko only
-  // sets nsMouseScrollEvent.scrollOverflow when it's processing
+  // sets WidgetMouseScrollEvent.scrollOverflow when it's processing
   // NS_MOUSE_PIXEL_SCROLL events (not NS_MOUSE_SCROLL events).
-  // nsMouseScrollEvent.scrollOverflow only indicates left or right overflow
+  // WidgetMouseScrollEvent.scrollOverflow only indicates left or right overflow
   // for horizontal NS_MOUSE_PIXEL_SCROLL events.
   if (!overflow) {
     return;