--- a/widget/windows/KeyboardLayout.cpp
+++ b/widget/windows/KeyboardLayout.cpp
@@ -3634,21 +3634,23 @@ KeyboardLayout::InitNativeKey(NativeKey&
       aNativeKey.mKeyNameIndex = KEY_NAME_INDEX_USE_STRING;
       aNativeKey.mCommittedCharsAndModifiers.
         Append(ch, aModKeyState.GetModifiers());
       return;
     }
   }
 
   uint8_t virtualKey = aNativeKey.mOriginalVirtualKeyCode;
-  int32_t virtualKeyIndex = GetKeyIndex(virtualKey);
-
-  if (virtualKeyIndex < 0) {
-    // Does not produce any printable characters, but still preserves the
-    // dead-key state.
+
+  // If the key is not a usual printable key, KeyboardLayout class assume that
+  // it's not cause dead char nor printable char.  Therefore, there are nothing
+  // to do here fore such keys (e.g., function keys).
+  // However, this should keep dead key state even if non-printable key is
+  // pressed during a dead key sequence.
+  if (!IsPrintableCharKey(virtualKey)) {
     return;
   }
 
   MOZ_ASSERT(virtualKey != VK_PACKET,
     "At handling VK_PACKET, we shouldn't refer keyboard layout");
   MOZ_ASSERT(aNativeKey.mKeyNameIndex == KEY_NAME_INDEX_USE_STRING,
     "Printable key's key name index must be KEY_NAME_INDEX_USE_STRING");
 
@@ -3660,17 +3662,17 @@ KeyboardLayout::InitNativeKey(NativeKey&
       //  First dead key event doesn't generate characters.
       if (isKeyDown) {
         // Dead-key state activated at keydown.
         mActiveDeadKey = virtualKey;
         mDeadKeyShiftState =
           VirtualKey::ModifierKeyStateToShiftState(aModKeyState);
       }
       UniCharsAndModifiers deadChars =
-        mVirtualKeys[virtualKeyIndex].GetNativeUniChars(aModKeyState);
+        GetNativeUniCharsAndModifiers(virtualKey, aModKeyState);
       NS_ASSERTION(deadChars.mLength == 1,
                    "dead key must generate only one character");
       aNativeKey.mKeyNameIndex = KEY_NAME_INDEX_Dead;
       return;
     }
 
     // At keydown message handling, we need to forget the first dead key
     // because there is no guarantee coming WM_KEYUP for the second dead
@@ -3795,16 +3797,30 @@ KeyboardLayout::GetUniCharsAndModifiers(
   UniCharsAndModifiers result;
   int32_t key = GetKeyIndex(aVirtualKey);
   if (key < 0) {
     return result;
   }
   return mVirtualKeys[key].GetUniChars(aShiftState);
 }
 
+UniCharsAndModifiers
+KeyboardLayout::GetNativeUniCharsAndModifiers(
+                  uint8_t aVirtualKey,
+                  const ModifierKeyState& aModKeyState) const
+{
+  int32_t key = GetKeyIndex(aVirtualKey);
+  if (key < 0) {
+    return UniCharsAndModifiers();
+  }
+  VirtualKey::ShiftState shiftState =
+    VirtualKey::ModifierKeyStateToShiftState(aModKeyState);
+  return mVirtualKeys[key].GetNativeUniChars(shiftState);
+}
+
 void
 KeyboardLayout::LoadLayout(HKL aLayout)
 {
   mIsPendingToRestoreKeyboardLayout = false;
 
   if (mKeyboardLayout == aLayout) {
     return;
   }

--- a/widget/windows/KeyboardLayout.h
+++ b/widget/windows/KeyboardLayout.h
@@ -694,31 +694,41 @@ public:
    * proper composite character when dead key produces a composite character.
    * Otherwise, just returns false.
    */
   bool MaybeInitNativeKeyWithCompositeChar(
          NativeKey& aNativeKey,
          const ModifierKeyState& aModKeyState);
 
   /**
-   * GetUniCharsAndModifiers() returns characters which is inputted by the
+   * GetUniCharsAndModifiers() returns characters which are inputted by
    * aVirtualKey with aModKeyState.  This method isn't stateful.
    * Note that if the combination causes text input, the result's Ctrl and
    * Alt key state are never active.
    */
   UniCharsAndModifiers GetUniCharsAndModifiers(
                          uint8_t aVirtualKey,
                          const ModifierKeyState& aModKeyState) const
   {
     VirtualKey::ShiftState shiftState =
       VirtualKey::ModifierKeyStateToShiftState(aModKeyState);
     return GetUniCharsAndModifiers(aVirtualKey, shiftState);
   }
 
   /**
+   * GetNativeUniCharsAndModifiers() returns characters which are inputted by
+   * aVirtualKey with aModKeyState.  The method isn't stateful.
+   * Note that different from GetUniCharsAndModifiers(), this returns
+   * actual modifier state of Ctrl and Alt.
+   */
+  UniCharsAndModifiers GetNativeUniCharsAndModifiers(
+                         uint8_t aVirtualKey,
+                         const ModifierKeyState& aModKeyState) const;
+
+  /**
    * OnLayoutChange() must be called before the first keydown message is
    * received.  LoadLayout() changes the keyboard state, that causes breaking
    * dead key state.  Therefore, we need to load the layout before the first
    * keydown message.
    */
   void OnLayoutChange(HKL aKeyboardLayout)
   {
     MOZ_ASSERT(!mIsOverridden);