diff --git a/content/base/src/Element.cpp b/content/base/src/Element.cpp
index b2f37e74ac3a..722bb8334394 100644
--- a/content/base/src/Element.cpp
+++ b/content/base/src/Element.cpp
@@ -2249,8 +2249,7 @@ Element::PostHandleEventForLinks(nsEventChainPostVisitor& aVisitor)
 
   case NS_MOUSE_CLICK:
     if (aVisitor.mEvent->IsLeftClickEvent()) {
-      WidgetInputEvent* inputEvent =
-        static_cast<WidgetInputEvent*>(aVisitor.mEvent);
+      WidgetInputEvent* inputEvent = aVisitor.mEvent->AsInputEvent();
       if (inputEvent->IsControl() || inputEvent->IsMeta() ||
           inputEvent->IsAlt() ||inputEvent->IsShift()) {
         break;
diff --git a/content/events/src/nsDOMEvent.cpp b/content/events/src/nsDOMEvent.cpp
index a2cf9229726d..30395fd668b0 100644
--- a/content/events/src/nsDOMEvent.cpp
+++ b/content/events/src/nsDOMEvent.cpp
@@ -526,7 +526,7 @@ nsDOMEvent::DuplicatePrivateData()
     }
     case NS_INPUT_EVENT:
     {
-      WidgetInputEvent* oldInputEvent = static_cast<WidgetInputEvent*>(mEvent);
+      WidgetInputEvent* oldInputEvent = mEvent->AsInputEvent();
       WidgetInputEvent* inputEvent = new WidgetInputEvent(false, msg, nullptr);
       inputEvent->AssignInputEventData(*oldInputEvent, true);
       newEvent = inputEvent;
diff --git a/content/events/src/nsDOMKeyboardEvent.cpp b/content/events/src/nsDOMKeyboardEvent.cpp
index c42c3f2a10ae..379ecb114337 100644
--- a/content/events/src/nsDOMKeyboardEvent.cpp
+++ b/content/events/src/nsDOMKeyboardEvent.cpp
@@ -33,6 +33,12 @@ NS_INTERFACE_MAP_BEGIN(nsDOMKeyboardEvent)
   NS_INTERFACE_MAP_ENTRY(nsIDOMKeyEvent)
 NS_INTERFACE_MAP_END_INHERITING(nsDOMUIEvent)
 
+bool
+nsDOMKeyboardEvent::AltKey()
+{
+  return mEvent->AsKeyboardEvent()->IsAlt();
+}
+
 NS_IMETHODIMP
 nsDOMKeyboardEvent::GetAltKey(bool* aIsDown)
 {
@@ -41,6 +47,12 @@ nsDOMKeyboardEvent::GetAltKey(bool* aIsDown)
   return NS_OK;
 }
 
+bool
+nsDOMKeyboardEvent::CtrlKey()
+{
+  return mEvent->AsKeyboardEvent()->IsControl();
+}
+
 NS_IMETHODIMP
 nsDOMKeyboardEvent::GetCtrlKey(bool* aIsDown)
 {
@@ -49,6 +61,12 @@ nsDOMKeyboardEvent::GetCtrlKey(bool* aIsDown)
   return NS_OK;
 }
 
+bool
+nsDOMKeyboardEvent::ShiftKey()
+{
+  return mEvent->AsKeyboardEvent()->IsShift();
+}
+
 NS_IMETHODIMP
 nsDOMKeyboardEvent::GetShiftKey(bool* aIsDown)
 {
@@ -57,6 +75,12 @@ nsDOMKeyboardEvent::GetShiftKey(bool* aIsDown)
   return NS_OK;
 }
 
+bool
+nsDOMKeyboardEvent::MetaKey()
+{
+  return mEvent->AsKeyboardEvent()->IsMeta();
+}
+
 NS_IMETHODIMP
 nsDOMKeyboardEvent::GetMetaKey(bool* aIsDown)
 {
diff --git a/content/events/src/nsDOMKeyboardEvent.h b/content/events/src/nsDOMKeyboardEvent.h
index 354d5821bc23..20d5df18621f 100644
--- a/content/events/src/nsDOMKeyboardEvent.h
+++ b/content/events/src/nsDOMKeyboardEvent.h
@@ -10,7 +10,6 @@
 #include "nsDOMUIEvent.h"
 #include "mozilla/EventForwards.h"
 #include "mozilla/dom/KeyboardEventBinding.h"
-#include "mozilla/BasicEvents.h"
 
 class nsDOMKeyboardEvent : public nsDOMUIEvent,
                            public nsIDOMKeyEvent
@@ -34,25 +33,10 @@ public:
     return mozilla::dom::KeyboardEventBinding::Wrap(aCx, aScope, this);
   }
 
-  bool AltKey()
-  {
-    return static_cast<mozilla::WidgetInputEvent*>(mEvent)->IsAlt();
-  }
-
-  bool CtrlKey()
-  {
-    return static_cast<mozilla::WidgetInputEvent*>(mEvent)->IsControl();
-  }
-
-  bool ShiftKey()
-  {
-    return static_cast<mozilla::WidgetInputEvent*>(mEvent)->IsShift();
-  }
-
-  bool MetaKey()
-  {
-    return static_cast<mozilla::WidgetInputEvent*>(mEvent)->IsMeta();
-  }
+  bool AltKey();
+  bool CtrlKey();
+  bool ShiftKey();
+  bool MetaKey();
 
   bool GetModifierState(const nsAString& aKey)
   {
diff --git a/content/events/src/nsDOMMouseEvent.cpp b/content/events/src/nsDOMMouseEvent.cpp
index c310d8453b7d..62116e75e6c8 100644
--- a/content/events/src/nsDOMMouseEvent.cpp
+++ b/content/events/src/nsDOMMouseEvent.cpp
@@ -122,7 +122,7 @@ nsDOMMouseEvent::InitMouseEvent(const nsAString& aType,
     case NS_WHEEL_EVENT:
     case NS_DRAG_EVENT:
     case NS_SIMPLE_GESTURE_EVENT:
-      static_cast<WidgetInputEvent*>(mEvent)->modifiers = modifiers;
+      mEvent->AsInputEvent()->modifiers = modifiers;
       return NS_OK;
     default:
       MOZ_CRASH("There is no space to store the modifiers");
@@ -354,6 +354,12 @@ nsDOMMouseEvent::ClientY()
                                      mClientPoint).y;
 }
 
+bool
+nsDOMMouseEvent::AltKey()
+{
+  return mEvent->AsInputEvent()->IsAlt();
+}
+
 NS_IMETHODIMP
 nsDOMMouseEvent::GetAltKey(bool* aIsDown)
 {
@@ -362,6 +368,12 @@ nsDOMMouseEvent::GetAltKey(bool* aIsDown)
   return NS_OK;
 }
 
+bool
+nsDOMMouseEvent::CtrlKey()
+{
+  return mEvent->AsInputEvent()->IsControl();
+}
+
 NS_IMETHODIMP
 nsDOMMouseEvent::GetCtrlKey(bool* aIsDown)
 {
@@ -370,6 +382,12 @@ nsDOMMouseEvent::GetCtrlKey(bool* aIsDown)
   return NS_OK;
 }
 
+bool
+nsDOMMouseEvent::ShiftKey()
+{
+  return mEvent->AsInputEvent()->IsShift();
+}
+
 NS_IMETHODIMP
 nsDOMMouseEvent::GetShiftKey(bool* aIsDown)
 {
@@ -378,6 +396,12 @@ nsDOMMouseEvent::GetShiftKey(bool* aIsDown)
   return NS_OK;
 }
 
+bool
+nsDOMMouseEvent::MetaKey()
+{
+  return mEvent->AsInputEvent()->IsMeta();
+}
+
 NS_IMETHODIMP
 nsDOMMouseEvent::GetMetaKey(bool* aIsDown)
 {
diff --git a/content/events/src/nsDOMMouseEvent.h b/content/events/src/nsDOMMouseEvent.h
index e84498cd35b9..4c6b179f1827 100644
--- a/content/events/src/nsDOMMouseEvent.h
+++ b/content/events/src/nsDOMMouseEvent.h
@@ -9,7 +9,7 @@
 #include "nsIDOMMouseEvent.h"
 #include "nsDOMUIEvent.h"
 #include "mozilla/dom/MouseEventBinding.h"
-#include "mozilla/BasicEvents.h"
+#include "mozilla/EventForwards.h"
 
 class nsDOMMouseEvent : public nsDOMUIEvent,
                         public nsIDOMMouseEvent
@@ -43,22 +43,10 @@ public:
   int32_t ScreenY();
   int32_t ClientX();
   int32_t ClientY();
-  bool CtrlKey()
-  {
-    return static_cast<mozilla::WidgetInputEvent*>(mEvent)->IsControl();
-  }
-  bool ShiftKey()
-  {
-    return static_cast<mozilla::WidgetInputEvent*>(mEvent)->IsShift();
-  }
-  bool AltKey()
-  {
-    return static_cast<mozilla::WidgetInputEvent*>(mEvent)->IsAlt();
-  }
-  bool MetaKey()
-  {
-    return static_cast<mozilla::WidgetInputEvent*>(mEvent)->IsMeta();
-  }
+  bool CtrlKey();
+  bool ShiftKey();
+  bool AltKey();
+  bool MetaKey();
   uint16_t Button();
   uint16_t Buttons();
   already_AddRefed<mozilla::dom::EventTarget> GetRelatedTarget();
diff --git a/content/events/src/nsDOMTouchEvent.cpp b/content/events/src/nsDOMTouchEvent.cpp
index c774a5b31793..9e2daf3678d7 100644
--- a/content/events/src/nsDOMTouchEvent.cpp
+++ b/content/events/src/nsDOMTouchEvent.cpp
@@ -107,8 +107,8 @@ nsDOMTouchEvent::InitTouchEvent(const nsAString& aType,
     return;
   }
 
-  static_cast<WidgetInputEvent*>(mEvent)->
-    InitBasicModifiers(aCtrlKey, aAltKey, aShiftKey, aMetaKey);
+  mEvent->AsInputEvent()->InitBasicModifiers(aCtrlKey, aAltKey,
+                                             aShiftKey, aMetaKey);
   mTouches = aTouches;
   mTargetTouches = aTargetTouches;
   mChangedTouches = aChangedTouches;
@@ -213,6 +213,30 @@ nsDOMTouchEvent::PrefEnabled()
   return prefValue;
 }
 
+bool
+nsDOMTouchEvent::AltKey()
+{
+  return mEvent->AsTouchEvent()->IsAlt();
+}
+
+bool
+nsDOMTouchEvent::MetaKey()
+{
+  return mEvent->AsTouchEvent()->IsMeta();
+}
+
+bool
+nsDOMTouchEvent::CtrlKey()
+{
+  return mEvent->AsTouchEvent()->IsControl();
+}
+
+bool
+nsDOMTouchEvent::ShiftKey()
+{
+  return mEvent->AsTouchEvent()->IsShift();
+}
+
 nsresult
 NS_NewDOMTouchEvent(nsIDOMEvent** aInstancePtrResult,
                     mozilla::dom::EventTarget* aOwner,
diff --git a/content/events/src/nsDOMTouchEvent.h b/content/events/src/nsDOMTouchEvent.h
index 02e6084c7847..2b28789d1071 100644
--- a/content/events/src/nsDOMTouchEvent.h
+++ b/content/events/src/nsDOMTouchEvent.h
@@ -8,8 +8,9 @@
 #include "nsDOMUIEvent.h"
 #include "nsTArray.h"
 #include "mozilla/Attributes.h"
-#include "mozilla/TouchEvents.h"
+#include "mozilla/EventForwards.h"
 #include "nsJSEnvironment.h"
+#include "mozilla/dom/Touch.h"
 #include "mozilla/dom/TouchEventBinding.h"
 #include "nsWrapperCache.h"
 
@@ -98,25 +99,10 @@ public:
   nsDOMTouchList* TargetTouches();
   nsDOMTouchList* ChangedTouches();
 
-  bool AltKey()
-  {
-    return static_cast<mozilla::WidgetInputEvent*>(mEvent)->IsAlt();
-  }
-
-  bool MetaKey()
-  {
-    return static_cast<mozilla::WidgetInputEvent*>(mEvent)->IsMeta();
-  }
-
-  bool CtrlKey()
-  {
-    return static_cast<mozilla::WidgetInputEvent*>(mEvent)->IsControl();
-  }
-
-  bool ShiftKey()
-  {
-    return static_cast<mozilla::WidgetInputEvent*>(mEvent)->IsShift();
-  }
+  bool AltKey();
+  bool MetaKey();
+  bool CtrlKey();
+  bool ShiftKey();
 
   void InitTouchEvent(const nsAString& aType,
                       bool aCanBubble,
diff --git a/content/events/src/nsDOMUIEvent.cpp b/content/events/src/nsDOMUIEvent.cpp
index b00fe263ae5c..136441d9f8e7 100644
--- a/content/events/src/nsDOMUIEvent.cpp
+++ b/content/events/src/nsDOMUIEvent.cpp
@@ -456,10 +456,8 @@ nsDOMUIEvent::ComputeModifierState(const nsAString& aModifiersList)
 bool
 nsDOMUIEvent::GetModifierStateInternal(const nsAString& aKey)
 {
-  if (!mEvent->IsInputDerivedEvent()) {
-    MOZ_CRASH("mEvent must be WidgetInputEvent or derived class");
-  }
-  WidgetInputEvent* inputEvent = static_cast<WidgetInputEvent*>(mEvent);
+  WidgetInputEvent* inputEvent = mEvent->AsInputEvent();
+  MOZ_ASSERT(inputEvent, "mEvent must be WidgetInputEvent or derived class");
   if (aKey.EqualsLiteral(NS_DOM_KEYNAME_SHIFT)) {
     return inputEvent->IsShift();
   }
diff --git a/content/events/src/nsDOMXULCommandEvent.cpp b/content/events/src/nsDOMXULCommandEvent.cpp
index f2233e61a7bd..ed10a4221d94 100644
--- a/content/events/src/nsDOMXULCommandEvent.cpp
+++ b/content/events/src/nsDOMXULCommandEvent.cpp
@@ -34,6 +34,12 @@ NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION_INHERITED(nsDOMXULCommandEvent)
   NS_INTERFACE_MAP_ENTRY(nsIDOMXULCommandEvent)
 NS_INTERFACE_MAP_END_INHERITING(nsDOMUIEvent)
 
+bool
+nsDOMXULCommandEvent::AltKey()
+{
+  return mEvent->AsInputEvent()->IsAlt();
+}
+
 NS_IMETHODIMP
 nsDOMXULCommandEvent::GetAltKey(bool* aIsDown)
 {
@@ -42,6 +48,12 @@ nsDOMXULCommandEvent::GetAltKey(bool* aIsDown)
   return NS_OK;
 }
 
+bool
+nsDOMXULCommandEvent::CtrlKey()
+{
+  return mEvent->AsInputEvent()->IsControl();
+}
+
 NS_IMETHODIMP
 nsDOMXULCommandEvent::GetCtrlKey(bool* aIsDown)
 {
@@ -50,6 +62,12 @@ nsDOMXULCommandEvent::GetCtrlKey(bool* aIsDown)
   return NS_OK;
 }
 
+bool
+nsDOMXULCommandEvent::ShiftKey()
+{
+  return mEvent->AsInputEvent()->IsShift();
+}
+
 NS_IMETHODIMP
 nsDOMXULCommandEvent::GetShiftKey(bool* aIsDown)
 {
@@ -58,6 +76,12 @@ nsDOMXULCommandEvent::GetShiftKey(bool* aIsDown)
   return NS_OK;
 }
 
+bool
+nsDOMXULCommandEvent::MetaKey()
+{
+  return mEvent->AsInputEvent()->IsMeta();
+}
+
 NS_IMETHODIMP
 nsDOMXULCommandEvent::GetMetaKey(bool* aIsDown)
 {
@@ -87,7 +111,8 @@ nsDOMXULCommandEvent::InitCommandEvent(const nsAString& aType,
                                           aView, aDetail);
   NS_ENSURE_SUCCESS(rv, rv);
 
-  Event()->InitBasicModifiers(aCtrlKey, aAltKey, aShiftKey, aMetaKey);
+  mEvent->AsInputEvent()->InitBasicModifiers(aCtrlKey, aAltKey,
+                                             aShiftKey, aMetaKey);
   mSourceEvent = aSourceEvent;
 
   return NS_OK;
diff --git a/content/events/src/nsDOMXULCommandEvent.h b/content/events/src/nsDOMXULCommandEvent.h
index 52f40f943caa..888d62d815e7 100644
--- a/content/events/src/nsDOMXULCommandEvent.h
+++ b/content/events/src/nsDOMXULCommandEvent.h
@@ -34,25 +34,10 @@ public:
     return mozilla::dom::XULCommandEventBinding::Wrap(aCx, aScope, this);
   }
 
-  bool AltKey()
-  {
-    return Event()->IsAlt();
-  }
-
-  bool CtrlKey()
-  {
-    return Event()->IsControl();
-  }
-
-  bool ShiftKey()
-  {
-    return Event()->IsShift();
-  }
-
-  bool MetaKey()
-  {
-    return Event()->IsMeta();
-  }
+  bool AltKey();
+  bool CtrlKey();
+  bool ShiftKey();
+  bool MetaKey();
 
   already_AddRefed<nsDOMEvent> GetSourceEvent()
   {
@@ -76,11 +61,6 @@ public:
   }
 
 protected:
-  // Convenience accessor for the event
-  mozilla::WidgetInputEvent* Event() {
-    return static_cast<mozilla::WidgetInputEvent*>(mEvent);
-  }
-
   nsCOMPtr<nsIDOMEvent> mSourceEvent;
 };
 
diff --git a/content/html/content/src/HTMLInputElement.cpp b/content/html/content/src/HTMLInputElement.cpp
index c993fd171d11..f518f516e6e5 100644
--- a/content/html/content/src/HTMLInputElement.cpp
+++ b/content/html/content/src/HTMLInputElement.cpp
@@ -3789,8 +3789,7 @@ HTMLInputElement::PostHandleEventForRangeThumb(nsEventChainPostVisitor& aVisitor
       if (nsIPresShell::GetCapturingContent()) {
         break; // don't start drag if someone else is already capturing
       }
-      WidgetInputEvent* inputEvent =
-        static_cast<WidgetInputEvent*>(aVisitor.mEvent);
+      WidgetInputEvent* inputEvent = aVisitor.mEvent->AsInputEvent();
       if (inputEvent->IsShift() || inputEvent->IsControl() ||
           inputEvent->IsAlt() || inputEvent->IsMeta() ||
           inputEvent->IsAltGraph() || inputEvent->IsFn() ||
@@ -3826,8 +3825,7 @@ HTMLInputElement::PostHandleEventForRangeThumb(nsEventChainPostVisitor& aVisitor
         break;
       }
       SetValueOfRangeForUserEvent(
-        rangeFrame->GetValueAtEventPoint(
-          static_cast<WidgetInputEvent*>(aVisitor.mEvent)));
+        rangeFrame->GetValueAtEventPoint(aVisitor.mEvent->AsInputEvent()));
       aVisitor.mEvent->mFlags.mMultipleActionsPrevented = true;
       break;
 
@@ -3840,7 +3838,7 @@ HTMLInputElement::PostHandleEventForRangeThumb(nsEventChainPostVisitor& aVisitor
       // call CancelRangeThumbDrag() if that is the case. We just finish off
       // the drag and set our final value (unless someone has called
       // preventDefault() and prevents us getting here).
-      FinishRangeThumbDrag(static_cast<WidgetInputEvent*>(aVisitor.mEvent));
+      FinishRangeThumbDrag(aVisitor.mEvent->AsInputEvent());
       aVisitor.mEvent->mFlags.mMultipleActionsPrevented = true;
       break;
 
diff --git a/content/html/content/src/HTMLLabelElement.cpp b/content/html/content/src/HTMLLabelElement.cpp
index f6693bb2a85f..56ff3ae6df96 100644
--- a/content/html/content/src/HTMLLabelElement.cpp
+++ b/content/html/content/src/HTMLLabelElement.cpp
@@ -197,7 +197,7 @@ HTMLLabelElement::PostHandleEvent(nsEventChainPostVisitor& aVisitor)
           EventFlags eventFlags;
           eventFlags.mMultipleActionsPrevented = true;
           DispatchClickEvent(aVisitor.mPresContext,
-                             static_cast<WidgetInputEvent*>(aVisitor.mEvent),
+                             aVisitor.mEvent->AsInputEvent(),
                              content, false, &eventFlags, &status);
           // Do we care about the status this returned?  I don't think we do...
           // Don't run another <label> off of this click
diff --git a/content/xbl/src/nsXBLPrototypeHandler.cpp b/content/xbl/src/nsXBLPrototypeHandler.cpp
index 56a2014d9b8b..59106100e797 100644
--- a/content/xbl/src/nsXBLPrototypeHandler.cpp
+++ b/content/xbl/src/nsXBLPrototypeHandler.cpp
@@ -910,9 +910,8 @@ bool
 nsXBLPrototypeHandler::ModifiersMatchMask(nsIDOMUIEvent* aEvent,
                                           bool aIgnoreShiftKey)
 {
-  WidgetEvent* event = aEvent->GetInternalNSEvent();
-  NS_ENSURE_TRUE(event && event->IsInputDerivedEvent(), false);
-  WidgetInputEvent* inputEvent = static_cast<WidgetInputEvent*>(event);
+  WidgetInputEvent* inputEvent = aEvent->GetInternalNSEvent()->AsInputEvent();
+  NS_ENSURE_TRUE(inputEvent, false);
 
   if (mKeyMask & cMetaMask) {
     if (inputEvent->IsMeta() != ((mKeyMask & cMeta) != 0)) {
diff --git a/content/xul/content/src/nsXULElement.cpp b/content/xul/content/src/nsXULElement.cpp
index 8a760f7e2c12..9217a2a6329b 100644
--- a/content/xul/content/src/nsXULElement.cpp
+++ b/content/xul/content/src/nsXULElement.cpp
@@ -1190,8 +1190,7 @@ nsXULElement::PreHandleEvent(nsEventChainPreVisitor& aVisitor)
                     }
                 }
 
-                WidgetInputEvent* orig =
-                    static_cast<WidgetInputEvent*>(aVisitor.mEvent);
+                WidgetInputEvent* orig = aVisitor.mEvent->AsInputEvent();
                 nsContentUtils::DispatchXULCommand(
                   commandContent,
                   aVisitor.mEvent->mFlags.mIsTrusted,
diff --git a/layout/generic/nsFrame.cpp b/layout/generic/nsFrame.cpp
index 420532a3fa66..bcd3d7aabcc1 100644
--- a/layout/generic/nsFrame.cpp
+++ b/layout/generic/nsFrame.cpp
@@ -2585,8 +2585,7 @@ nsFrame::HandlePress(nsPresContext* aPresContext,
   //weaaak. only the editor can display frame selection not just text and images
   isEditor = isEditor == nsISelectionDisplay::DISPLAY_ALL;
 
-  WidgetInputEvent* keyEvent = static_cast<WidgetInputEvent*>(aEvent);
-  if (!keyEvent->IsAlt()) {
+  if (!aEvent->AsInputEvent()->IsAlt()) {
     for (nsIContent* content = mContent; content;
          content = content->GetParent()) {
       if (nsContentUtils::ContentIsDraggable(content) &&
diff --git a/layout/xul/base/src/nsButtonBoxFrame.cpp b/layout/xul/base/src/nsButtonBoxFrame.cpp
index 3a43b49ee07c..03a6997849c8 100644
--- a/layout/xul/base/src/nsButtonBoxFrame.cpp
+++ b/layout/xul/base/src/nsButtonBoxFrame.cpp
@@ -132,10 +132,11 @@ nsButtonBoxFrame::DoMouseClick(WidgetGUIEvent* aEvent, bool aTrustEvent)
   bool isAlt = false;
   bool isMeta = false;
   if(aEvent) {
-    isShift = static_cast<WidgetInputEvent*>(aEvent)->IsShift();
-    isControl = static_cast<WidgetInputEvent*>(aEvent)->IsControl();
-    isAlt = static_cast<WidgetInputEvent*>(aEvent)->IsAlt();
-    isMeta = static_cast<WidgetInputEvent*>(aEvent)->IsMeta();
+    WidgetInputEvent* inputEvent = aEvent->AsInputEvent();
+    isShift = inputEvent->IsShift();
+    isControl = inputEvent->IsControl();
+    isAlt = inputEvent->IsAlt();
+    isMeta = inputEvent->IsMeta();
   }
 
   // Have the content handle the event, propagating it according to normal DOM rules.
diff --git a/layout/xul/base/src/nsMenuBarListener.cpp b/layout/xul/base/src/nsMenuBarListener.cpp
index a2baa1ef1b32..75095d6af59e 100644
--- a/layout/xul/base/src/nsMenuBarListener.cpp
+++ b/layout/xul/base/src/nsMenuBarListener.cpp
@@ -270,7 +270,7 @@ nsMenuBarListener::GetModifiers(nsIDOMKeyEvent* aKeyEvent)
 {
   uint32_t modifiers = 0;
   WidgetInputEvent* inputEvent =
-    static_cast<WidgetInputEvent*>(aKeyEvent->GetInternalNSEvent());
+    aKeyEvent->GetInternalNSEvent()->AsInputEvent();
   MOZ_ASSERT(inputEvent);
 
   if (inputEvent->IsShift()) {
diff --git a/layout/xul/base/src/nsMenuFrame.cpp b/layout/xul/base/src/nsMenuFrame.cpp
index 69e94d61733c..936da64b16d5 100644
--- a/layout/xul/base/src/nsMenuFrame.cpp
+++ b/layout/xul/base/src/nsMenuFrame.cpp
@@ -1248,12 +1248,12 @@ nsMenuFrame::CreateMenuCommandEvent(WidgetGUIEvent* aEvent, bool aFlipChecked)
                               nsContentUtils::IsCallerChrome();
 
   bool shift = false, control = false, alt = false, meta = false;
-  if (aEvent && (aEvent->eventStructType == NS_MOUSE_EVENT ||
-                 aEvent->eventStructType == NS_KEY_EVENT)) {
-    shift = static_cast<WidgetInputEvent*>(aEvent)->IsShift();
-    control = static_cast<WidgetInputEvent*>(aEvent)->IsControl();
-    alt = static_cast<WidgetInputEvent*>(aEvent)->IsAlt();
-    meta = static_cast<WidgetInputEvent*>(aEvent)->IsMeta();
+  WidgetInputEvent* inputEvent = aEvent ? aEvent->AsInputEvent() : nullptr;
+  if (inputEvent) {
+    shift = inputEvent->IsShift();
+    control = inputEvent->IsControl();
+    alt = inputEvent->IsAlt();
+    meta = inputEvent->IsMeta();
   }
 
   // Because the command event is firing asynchronously, a flag is needed to
diff --git a/layout/xul/base/src/nsXULPopupManager.cpp b/layout/xul/base/src/nsXULPopupManager.cpp
index ade01bc5f43c..dcf8aeabe77b 100644
--- a/layout/xul/base/src/nsXULPopupManager.cpp
+++ b/layout/xul/base/src/nsXULPopupManager.cpp
@@ -480,9 +480,9 @@ nsXULPopupManager::InitTriggerEvent(nsIDOMEvent* aEvent, nsIContent* aPopup,
     NS_ASSERTION(aPopup, "Expected a popup node");
     WidgetEvent* event = aEvent->GetInternalNSEvent();
     if (event) {
-      if (event->eventStructType == NS_MOUSE_EVENT ||
-          event->eventStructType == NS_KEY_EVENT) {
-        mCachedModifiers = static_cast<WidgetInputEvent*>(event)->modifiers;
+      WidgetInputEvent* inputEvent = event->AsInputEvent();
+      if (inputEvent) {
+        mCachedModifiers = inputEvent->modifiers;
       }
       nsIDocument* doc = aPopup->GetCurrentDoc();
       if (doc) {
diff --git a/widget/cocoa/TextInputHandler.mm b/widget/cocoa/TextInputHandler.mm
index cd9a9af69e83..73cf763cad69 100644
--- a/widget/cocoa/TextInputHandler.mm
+++ b/widget/cocoa/TextInputHandler.mm
@@ -4179,7 +4179,7 @@ bool
 TextInputHandlerBase::DispatchEvent(WidgetGUIEvent& aEvent)
 {
   if (aEvent.message == NS_KEY_PRESS) {
-    WidgetInputEvent& inputEvent = static_cast<WidgetInputEvent&>(aEvent);
+    WidgetInputEvent& inputEvent = *aEvent.AsInputEvent();
     if (!inputEvent.IsMeta()) {
       PR_LOG(gLog, PR_LOG_ALWAYS,
         ("%p TextInputHandlerBase::DispatchEvent, hiding mouse cursor", this));
diff --git a/widget/windows/winrt/MetroWidget.cpp b/widget/windows/winrt/MetroWidget.cpp
index c2281f0fcc23..198c28a23083 100644
--- a/widget/windows/winrt/MetroWidget.cpp
+++ b/widget/windows/winrt/MetroWidget.cpp
@@ -1020,8 +1020,7 @@ MetroWidget::ApzReceiveInputEvent(WidgetInputEvent* aEvent)
   if (!MetroWidget::sAPZC) {
     return nsEventStatus_eIgnore;
   }
-  WidgetInputEvent& event = static_cast<WidgetInputEvent&>(*aEvent);
-  return MetroWidget::sAPZC->ReceiveInputEvent(event);
+  return MetroWidget::sAPZC->ReceiveInputEvent(*aEvent->AsInputEvent());
 }
 
 nsEventStatus
@@ -1034,8 +1033,8 @@ MetroWidget::ApzReceiveInputEvent(WidgetInputEvent* aInEvent,
   if (!MetroWidget::sAPZC) {
     return nsEventStatus_eIgnore;
   }
-  WidgetInputEvent& event = static_cast<WidgetInputEvent&>(*aInEvent);
-  return MetroWidget::sAPZC->ReceiveInputEvent(event, aOutEvent);
+  return MetroWidget::sAPZC->ReceiveInputEvent(*aInEvent->AsInputEvent(),
+                                               aOutEvent);
 }
 
 LayerManager*