--- a/widget/windows/KeyboardLayout.cpp
+++ b/widget/windows/KeyboardLayout.cpp
@@ -844,16 +844,17 @@ uint8_t NativeKey::sDispatchedKeyOfAppCo
 NativeKey::NativeKey(nsWindowBase* aWidget,
                      const MSG& aMessage,
                      const ModifierKeyState& aModKeyState,
                      HKL aOverrideKeyboardLayout,
                      nsTArray<FakeCharMsg>* aFakeCharMsgs)
   : mWidget(aWidget)
   , mDispatcher(aWidget->GetTextEventDispatcher())
   , mMsg(aMessage)
+  , mFocusedWndBeforeDispatch(::GetFocus())
   , mDOMKeyCode(0)
   , mKeyNameIndex(KEY_NAME_INDEX_Unidentified)
   , mCodeNameIndex(CODE_NAME_INDEX_UNKNOWN)
   , mModKeyState(aModKeyState)
   , mVirtualKeyCode(0)
   , mOriginalVirtualKeyCode(0)
   , mShiftedLatinChar(0)
   , mUnshiftedLatinChar(0)
@@ -1740,17 +1741,17 @@ NativeKey::HandleKeyDownMessage(bool* aE
     defaultPrevented = status == nsEventStatus_eConsumeNoDefault;
 
     // We don't need to handle key messages on plugin for eKeyPress since
     // eKeyDownOnPlugin is handled as both eKeyDown and eKeyPress.
     if (IsKeyMessageOnPlugin()) {
       return defaultPrevented;
     }
 
-    if (mWidget->Destroyed()) {
+    if (mWidget->Destroyed() || IsFocusedWindowChanged()) {
       return true;
     }
 
     // If IMC wasn't associated to the window but is associated it now (i.e.,
     // focus is moved from a non-editable editor to an editor by keydown
     // event handler), WM_CHAR and WM_SYSCHAR shouldn't cause first character
     // inputting if IME is opened.  But then, we should redirect the native
     // keydown message to IME.
@@ -1812,17 +1813,17 @@ NativeKey::HandleKeyDownMessage(bool* aE
   }
 
   if (!mFollowingCharMsgs.IsEmpty()) {
     bool consumed = false;
     for (size_t i = 0; i < mFollowingCharMsgs.Length(); ++i) {
       consumed =
         DispatchKeyPressEventForFollowingCharMessage(mFollowingCharMsgs[i]) ||
         consumed;
-      if (mWidget->Destroyed()) {
+      if (mWidget->Destroyed() || IsFocusedWindowChanged()) {
         return true;
       }
     }
     return consumed;
   }
 
   // If WM_KEYDOWN of VK_PACKET isn't followed by WM_CHAR, we don't need to
   // dispatch keypress events.
@@ -2352,17 +2353,17 @@ NativeKey::DispatchPluginEventsAndDiscar
   MOZ_ASSERT(!IsKeyMessageOnPlugin());
 
   bool anyCharMessagesRemoved = false;
   for (size_t i = 0; i < mFollowingCharMsgs.Length(); ++i) {
     anyCharMessagesRemoved = true;
     MOZ_RELEASE_ASSERT(!mWidget->Destroyed(),
       "NativeKey tries to dispatch a plugin event on destroyed widget");
     mWidget->DispatchPluginEvent(mFollowingCharMsgs[i]);
-    if (mWidget->Destroyed()) {
+    if (mWidget->Destroyed() || IsFocusedWindowChanged()) {
       return true;
     }
   }
 
   if (!mFakeCharMsgs && !anyCharMessagesRemoved &&
       mDOMKeyCode == NS_VK_BACK && IsIMEDoingKakuteiUndo()) {
     // This is for a hack for ATOK and WXG.  So, PeekMessage() must scceed!
     MSG msg;

--- a/widget/windows/KeyboardLayout.h
+++ b/widget/windows/KeyboardLayout.h
@@ -262,16 +262,20 @@ private:
   RefPtr<nsWindowBase> mWidget;
   RefPtr<TextEventDispatcher> mDispatcher;
   HKL mKeyboardLayout;
   MSG mMsg;
   // mFollowingCharMsgs stores WM_CHAR, WM_SYSCHAR, WM_DEADCHAR or
   // WM_SYSDEADCHAR message which follows WM_KEYDOWN.
   // Note that the stored messaged are already removed from the queue.
   nsTArray<MSG> mFollowingCharMsgs;
+  // If dispatching eKeyDown or eKeyPress event causes focus change,
+  // the instance shouldn't handle remaning char messages.  For checking it,
+  // this should store first focused window.
+  HWND mFocusedWndBeforeDispatch;
 
   uint32_t mDOMKeyCode;
   KeyNameIndex mKeyNameIndex;
   CodeNameIndex mCodeNameIndex;
 
   ModifierKeyState mModKeyState;
 
   // mVirtualKeyCode distinguishes left key or right key of modifier key.
@@ -521,16 +525,25 @@ private:
   bool NeedsToHandleWithoutFollowingCharMessages() const;
 
   /**
    * ComputeInputtingStringWithKeyboardLayout() computes string to be inputted
    * with the key and the modifier state, without shift state and with shift
    * state.
    */
   void ComputeInputtingStringWithKeyboardLayout();
+
+  /**
+   * IsFocusedWindowChanged() returns true if focused window is changed
+   * after the instance is created.
+   */
+  bool IsFocusedWindowChanged() const
+  {
+    return mFocusedWndBeforeDispatch != ::GetFocus();
+  }
 };
 
 class KeyboardLayout
 {
   friend class NativeKey;
 
 private:
   KeyboardLayout();