diff --git a/widget/nsIWidget.h b/widget/nsIWidget.h
index 7fae7b90bea4..7fe02a854763 100644
--- a/widget/nsIWidget.h
+++ b/widget/nsIWidget.h
@@ -1861,13 +1861,6 @@ class nsIWidget : public nsISupports {
    */
   virtual void SetPluginFocused(bool& aFocused) = 0;
 
-  /*
-   * Tell the plugin has focus.  It is unnecessary to use IPC
-   */
-  bool PluginHasFocus() {
-    return GetInputContext().mIMEState.mEnabled == IMEEnabled::Plugin;
-  }
-
   /*
    * Enable or Disable IME by windowless plugin.
    */
diff --git a/widget/windows/IMMHandler.cpp b/widget/windows/IMMHandler.cpp
index ed847c89b18a..338c3a64fdd5 100644
--- a/widget/windows/IMMHandler.cpp
+++ b/widget/windows/IMMHandler.cpp
@@ -487,10 +487,6 @@ void IMMHandler::OnUpdateComposition(nsWindow* aWindow) {
     return;
   }
 
-  if (aWindow->PluginHasFocus()) {
-    return;
-  }
-
   IMEContext context(aWindow);
   gIMMHandler->SetIMERelatedWindowsPos(aWindow, context);
 }
@@ -2168,8 +2164,7 @@ void IMMHandler::AdjustCompositionFont(nsWindow* aWindow,
   logFont.lfClipPrecision = CLIP_DEFAULT_PRECIS;
   logFont.lfPitchAndFamily = DEFAULT_PITCH;
 
-  if (!aWindow->PluginHasFocus() && aWritingMode.IsVertical() &&
-      IsVerticalWritingSupported()) {
+  if (aWritingMode.IsVertical() && IsVerticalWritingSupported()) {
     SetVerticalFontToLogFont(IsJapanist2003Active()
                                  ? sCompositionFontForJapanist2003
                                  : sCompositionFont,
diff --git a/widget/windows/KeyboardLayout.cpp b/widget/windows/KeyboardLayout.cpp
index 51af7cbeccdf..220c578b1656 100644
--- a/widget/windows/KeyboardLayout.cpp
+++ b/widget/windows/KeyboardLayout.cpp
@@ -2532,7 +2532,7 @@ bool NativeKey::HandleKeyDownMessage(bool* aEventDispatched) const {
     // message is processed by us, so, nobody shouldn't process it.
     HWND focusedWnd = ::GetFocus();
     if (!defaultPrevented && !mFakeCharMsgs && !IsKeyMessageOnPlugin() &&
-        focusedWnd && !mWidget->PluginHasFocus() && !isIMEEnabled &&
+        focusedWnd && !isIMEEnabled &&
         WinUtils::IsIMEEnabled(mWidget->GetInputContext())) {
       RedirectedKeyDownMessageManager::RemoveNextCharMessage(focusedWnd);
 
@@ -2598,7 +2598,6 @@ bool NativeKey::HandleKeyDownMessage(bool* aEventDispatched) const {
             ("%p   NativeKey::HandleKeyDownMessage(), not dispatching keypress "
              "event because preceding keydown event was consumed",
              this));
-    MaybeDispatchPluginEventsForRemovedCharMessages();
     return true;
   }
 
@@ -2623,8 +2622,7 @@ bool NativeKey::HandleKeyDownMessage(bool* aEventDispatched) const {
             ("%p   NativeKey::HandleKeyDownMessage(), tries to be dispatching "
              "keypress events...",
              this));
-    return (MaybeDispatchPluginEventsForRemovedCharMessages() ||
-            DispatchKeyPressEventsWithoutCharMessage());
+    return DispatchKeyPressEventsWithoutCharMessage();
   }
 
   // If WM_KEYDOWN of VK_PACKET isn't followed by WM_CHAR, we don't need to
@@ -3403,71 +3401,6 @@ bool NativeKey::GetFollowingCharMessage(MSG& aCharMsg) {
   return false;
 }
 
-bool NativeKey::MaybeDispatchPluginEventsForRemovedCharMessages() const {
-  MOZ_ASSERT(IsKeyDownMessage());
-  MOZ_ASSERT(!IsKeyMessageOnPlugin());
-
-  for (size_t i = 0;
-       i < mFollowingCharMsgs.Length() && mWidget->ShouldDispatchPluginEvent();
-       ++i) {
-    MOZ_LOG(
-        sNativeKeyLogger, LogLevel::Info,
-        ("%p   NativeKey::MaybeDispatchPluginEventsForRemovedCharMessages(), "
-         "dispatching %uth plugin event for %s...",
-         this, i + 1, ToString(mFollowingCharMsgs[i]).get()));
-    MOZ_RELEASE_ASSERT(
-        !mWidget->Destroyed(),
-        "NativeKey tries to dispatch a plugin event on destroyed widget");
-    mWidget->DispatchPluginEvent(mFollowingCharMsgs[i]);
-    if (mWidget->Destroyed() || IsFocusedWindowChanged()) {
-      MOZ_LOG(
-          sNativeKeyLogger, LogLevel::Info,
-          ("%p   NativeKey::MaybeDispatchPluginEventsForRemovedCharMessages(), "
-           "%uth plugin event caused %s",
-           this, i + 1,
-           mWidget->Destroyed() ? "destroying the widget" : "focus change"));
-      return true;
-    }
-    MOZ_LOG(
-        sNativeKeyLogger, LogLevel::Info,
-        ("%p   NativeKey::MaybeDispatchPluginEventsForRemovedCharMessages(), "
-         "dispatched %uth plugin event",
-         this, i + 1));
-  }
-
-  // Dispatch odd char messages which are caused by ATOK or WXG (both of them
-  // are Japanese IME) and removed by RemoveFollowingOddCharMessages().
-  for (size_t i = 0;
-       i < mRemovedOddCharMsgs.Length() && mWidget->ShouldDispatchPluginEvent();
-       ++i) {
-    MOZ_LOG(
-        sNativeKeyLogger, LogLevel::Info,
-        ("%p   NativeKey::MaybeDispatchPluginEventsForRemovedCharMessages(), "
-         "dispatching %uth plugin event for odd char message, %s...",
-         this, i + 1, ToString(mFollowingCharMsgs[i]).get()));
-    MOZ_RELEASE_ASSERT(
-        !mWidget->Destroyed(),
-        "NativeKey tries to dispatch a plugin event on destroyed widget");
-    mWidget->DispatchPluginEvent(mRemovedOddCharMsgs[i]);
-    if (mWidget->Destroyed() || IsFocusedWindowChanged()) {
-      MOZ_LOG(
-          sNativeKeyLogger, LogLevel::Info,
-          ("%p   NativeKey::MaybeDispatchPluginEventsForRemovedCharMessages(), "
-           "%uth plugin event for odd char message caused %s",
-           this, i + 1,
-           mWidget->Destroyed() ? "destroying the widget" : "focus change"));
-      return true;
-    }
-    MOZ_LOG(
-        sNativeKeyLogger, LogLevel::Info,
-        ("%p   NativeKey::MaybeDispatchPluginEventsForRemovedCharMessages(), "
-         "dispatched %uth plugin event for odd char message",
-         this, i + 1));
-  }
-
-  return false;
-}
-
 void NativeKey::ComputeInputtingStringWithKeyboardLayout() {
   KeyboardLayout* keyboardLayout = KeyboardLayout::GetInstance();
 
diff --git a/widget/windows/KeyboardLayout.h b/widget/windows/KeyboardLayout.h
index cce1865eecde..d5b4cbb509d7 100644
--- a/widget/windows/KeyboardLayout.h
+++ b/widget/windows/KeyboardLayout.h
@@ -753,14 +753,6 @@ class MOZ_STACK_CLASS NativeKey final {
    */
   bool DispatchKeyPressEventsWithoutCharMessage() const;
 
-  /**
-   * MaybeDispatchPluginEventsForRemovedCharMessages() dispatches plugin events
-   * for removed char messages when a windowless plugin has focus.
-   * Returns true if the widget is destroyed or blurred during dispatching a
-   * plugin event.
-   */
-  bool MaybeDispatchPluginEventsForRemovedCharMessages() const;
-
   /**
    * Checkes whether the key event down message is handled without following
    * WM_CHAR messages.  For example, if following WM_CHAR message indicates
diff --git a/widget/windows/nsWindowBase.cpp b/widget/windows/nsWindowBase.cpp
index 0d3cd6a6d336..a9c9d2b53ec3 100644
--- a/widget/windows/nsWindowBase.cpp
+++ b/widget/windows/nsWindowBase.cpp
@@ -19,23 +19,7 @@ static const wchar_t kUser32LibName[] = L"user32.dll";
 bool nsWindowBase::sTouchInjectInitialized = false;
 InjectTouchInputPtr nsWindowBase::sInjectTouchFuncPtr;
 
-bool nsWindowBase::DispatchPluginEvent(const MSG& aMsg) {
-  if (!ShouldDispatchPluginEvent()) {
-    return false;
-  }
-  WidgetPluginEvent pluginEvent(true, ePluginInputEvent, this);
-  LayoutDeviceIntPoint point(0, 0);
-  InitEvent(pluginEvent, &point);
-  NPEvent npEvent;
-  npEvent.event = aMsg.message;
-  npEvent.wParam = aMsg.wParam;
-  npEvent.lParam = aMsg.lParam;
-  pluginEvent.mPluginEvent.Copy(npEvent);
-  pluginEvent.mRetargetToFocusedDocument = true;
-  return DispatchWindowEvent(&pluginEvent);
-}
-
-bool nsWindowBase::ShouldDispatchPluginEvent() { return PluginHasFocus(); }
+bool nsWindowBase::DispatchPluginEvent(const MSG& aMsg) { return false; }
 
 // static
 bool nsWindowBase::InitTouchInjection() {
diff --git a/widget/windows/nsWindowBase.h b/widget/windows/nsWindowBase.h
index 69f043c05049..02a91b0b7cbf 100644
--- a/widget/windows/nsWindowBase.h
+++ b/widget/windows/nsWindowBase.h
@@ -85,11 +85,6 @@ class nsWindowBase : public nsBaseWidget {
    */
   virtual bool DispatchPluginEvent(const MSG& aMsg);
 
-  /*
-   * Returns true if this should dispatch a plugin event.
-   */
-  bool ShouldDispatchPluginEvent();
-
   /*
    * Touch input injection apis
    */