--- a/dom/events/IMEStateManager.cpp
+++ b/dom/events/IMEStateManager.cpp
@@ -938,17 +938,17 @@ IMEStateManager::DispatchCompositionEven
   //       following commit events in TextComposition::DispatchEvent().
   //       However, if commit or cancel for a request is performed synchronously
   //       during not safe to dispatch events, PresShell must have discarded
   //       compositionend event.  Then, the synthesized compositionend event is
   //       the last event for the composition.  In this case, we need to
   //       destroy the TextComposition with synthesized compositionend event.
   if ((!aIsSynthesized ||
        composition->WasNativeCompositionEndEventDiscarded()) &&
-      aCompositionEvent->message == NS_COMPOSITION_END) {
+      aCompositionEvent->CausesDOMCompositionEndEvent()) {
     TextCompositionArray::index_type i =
       sTextCompositions->IndexOf(aCompositionEvent->widget);
     if (i != TextCompositionArray::NoIndex) {
       PR_LOG(sISMLog, PR_LOG_DEBUG,
         ("ISM:   IMEStateManager::DispatchCompositionEvent(), "
          "removing TextComposition from the array since NS_COMPOSTION_END "
          "was dispatched"));
       sTextCompositions->ElementAt(i)->Destroy();

--- a/dom/events/TextComposition.cpp
+++ b/dom/events/TextComposition.cpp
@@ -117,17 +117,17 @@ TextComposition::OnCompositionEventDisca
 
   MOZ_ASSERT(aCompositionEvent->mFlags.mIsTrusted,
              "Shouldn't be called with untrusted event");
 
   // XXX If composition events are discarded, should we dispatch them with
   //     runnable event?  However, even if we do so, it might make native IME
   //     confused due to async modification.  Especially when native IME is
   //     TSF.
-  if (aCompositionEvent->message != NS_COMPOSITION_END) {
+  if (!aCompositionEvent->CausesDOMCompositionEndEvent()) {
     return;
   }
 
   mWasNativeCompositionEndEventDiscarded = true;
 }
 
 void
 TextComposition::DispatchCompositionEvent(
@@ -180,38 +180,38 @@ TextComposition::DispatchCompositionEven
           mLastData != IDEOGRAPHIC_SPACE) {
         committingData->Assign(mLastData);
       } else if (mIsRequestingCancel && !committingData->IsEmpty()) {
         committingData->Truncate();
       }
     }
   }
 
-  if (aCompositionEvent->message == NS_COMPOSITION_CHANGE) {
+  if (aCompositionEvent->CausesDOMTextEvent()) {
     if (!MaybeDispatchCompositionUpdate(aCompositionEvent)) {
       return;
     }
   }
 
   EventDispatcher::Dispatch(mNode, mPresContext,
                             aCompositionEvent, nullptr, aStatus, aCallBack);
 
   if (!IsValidStateForComposition(aCompositionEvent->widget)) {
     return;
   }
 
   // Emulate editor behavior of compositionchange event (DOM text event) handler
   // if no editor handles composition events.
-  if (aCompositionEvent->message == NS_COMPOSITION_CHANGE && !HasEditor()) {
+  if (aCompositionEvent->CausesDOMTextEvent() && !HasEditor()) {
     EditorWillHandleCompositionChangeEvent(aCompositionEvent);
     EditorDidHandleCompositionChangeEvent();
   }
 
 #ifdef DEBUG
-  else if (aCompositionEvent->message == NS_COMPOSITION_END) {
+  else if (aCompositionEvent->CausesDOMCompositionEndEvent()) {
     MOZ_ASSERT(!mIsComposing, "Why is the editor still composing?");
     MOZ_ASSERT(!HasEditor(), "Why does the editor still keep to hold this?");
   }
 #endif // #ifdef DEBUG
 
   // Notify composition update to widget if possible
   NotityUpdateComposition(aCompositionEvent);
 }
@@ -235,17 +235,17 @@ TextComposition::NotityUpdateComposition
     if (selectedTextEvent.mSucceeded) {
       mCompositionStartOffset = selectedTextEvent.mReply.mOffset;
     } else {
       // Unknown offset
       NS_WARNING("Cannot get start offset of IME composition");
       mCompositionStartOffset = 0;
     }
     mCompositionTargetOffset = mCompositionStartOffset;
-  } else if (aCompositionEvent->message == NS_COMPOSITION_CHANGE) {
+  } else if (aCompositionEvent->CausesDOMTextEvent()) {
     mCompositionTargetOffset =
       mCompositionStartOffset + aCompositionEvent->TargetClauseOffset();
   } else {
     return;
   }
 
   NotifyIME(NOTIFY_IME_OF_COMPOSITION_UPDATE);
 }

--- a/dom/ipc/TabParent.cpp
+++ b/dom/ipc/TabParent.cpp
@@ -1633,21 +1633,21 @@ TabParent::HandleQueryContentEvent(Widge
 
 bool
 TabParent::SendCompositionEvent(WidgetCompositionEvent& event)
 {
   if (mIsDestroyed) {
     return false;
   }
 
-  if (event.message == NS_COMPOSITION_CHANGE) {
+  if (event.CausesDOMTextEvent()) {
     return SendCompositionChangeEvent(event);
   }
 
-  mIMEComposing = event.message != NS_COMPOSITION_END;
+  mIMEComposing = !event.CausesDOMCompositionEndEvent();
   mIMECompositionStart = std::min(mIMESelectionAnchor, mIMESelectionFocus);
   if (mIMECompositionEnding)
     return true;
   event.mSeqno = ++mIMESeqno;
   return PBrowserParent::SendCompositionEvent(event);
 }
 
 /**
@@ -1668,16 +1668,17 @@ TabParent::SendCompositionChangeEvent(Wi
 
   // We must be able to simulate the selection because
   // we might not receive selection updates in time
   if (!mIMEComposing) {
     mIMECompositionStart = std::min(mIMESelectionAnchor, mIMESelectionFocus);
   }
   mIMESelectionAnchor = mIMESelectionFocus =
       mIMECompositionStart + event.mData.Length();
+  mIMEComposing = !event.CausesDOMCompositionEndEvent();
 
   event.mSeqno = ++mIMESeqno;
   return PBrowserParent::SendCompositionEvent(event);
 }
 
 bool
 TabParent::SendSelectionEvent(WidgetSelectionEvent& event)
 {

--- a/widget/PuppetWidget.cpp
+++ b/widget/PuppetWidget.cpp
@@ -326,17 +326,18 @@ PuppetWidget::DispatchEvent(WidgetGUIEve
       return NS_OK;
     }
   }
 
   if (mAttachedWidgetListener) {
     aStatus = mAttachedWidgetListener->HandleEvent(event, mUseAttachedEvents);
   }
 
-  if (event->message == NS_COMPOSITION_END) {
+  if (event->mClass == eCompositionEventClass &&
+      event->AsCompositionEvent()->CausesDOMCompositionEndEvent()) {
     mIMEComposing = false;
   }
 
   return NS_OK;
 }
 
 
 NS_IMETHODIMP_(bool)

--- a/widget/TextEvents.h
+++ b/widget/TextEvents.h
@@ -337,16 +337,26 @@ public:
   {
     return mRanges ? mRanges->TargetClauseOffset() : 0;
   }
 
   uint32_t RangeCount() const
   {
     return mRanges ? mRanges->Length() : 0;
   }
+
+  bool CausesDOMTextEvent() const
+  {
+    return message == NS_COMPOSITION_CHANGE;
+  }
+
+  bool CausesDOMCompositionEndEvent() const
+  {
+    return message == NS_COMPOSITION_END;
+  }
 };
 
 /******************************************************************************
  * mozilla::WidgetQueryContentEvent
  ******************************************************************************/
 
 class WidgetQueryContentEvent : public WidgetGUIEvent
 {