diff --git a/widget/tests/gtest/TestWinInputPane.cpp b/widget/tests/gtest/TestWinInputPane.cpp
deleted file mode 100644
index 4876150b931b..000000000000
--- a/widget/tests/gtest/TestWinInputPane.cpp
+++ /dev/null
@@ -1,51 +0,0 @@
-/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
-/* vim: set ts=8 sts=2 et sw=2 tw=80: */
-/* This Source Code Form is subject to the terms of the Mozilla Public
- * License, v. 2.0. If a copy of the MPL was not distributed with this
- * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
-
-#include "gtest/gtest.h"
-
-#include <windows.h>
-
-#include "MockWinWidget.h"
-#include "mozilla/widget/OSKInputPaneManager.h"
-
-using namespace mozilla;
-using namespace mozilla::widget;
-
-class WinInputPaneTest : public ::testing::Test {
- protected:
-  HWND CreateNativeWindow(DWORD aStyle, DWORD aExStyle) {
-    mMockWinWidget =
-        MockWinWidget::Create(WS_OVERLAPPEDWINDOW | WS_CLIPCHILDREN | aStyle,
-                              aExStyle, LayoutDeviceIntRect(0, 0, 100, 100));
-    EXPECT_NE(nullptr, mMockWinWidget.get());
-    HWND hwnd = mMockWinWidget->GetWnd();
-
-    ::ShowWindow(hwnd, SW_SHOWNORMAL);
-    EXPECT_TRUE(UpdateWindow(hwnd));
-    return hwnd;
-  }
-
-  void ExpectHasEventHandler(HWND aHwnd, bool aValue) {
-    Maybe<bool> hasEventHandler =
-        OSKInputPaneManager::HasInputPaneEventHandlerService(aHwnd);
-    EXPECT_TRUE(hasEventHandler.isSome() && hasEventHandler.value() == aValue);
-  }
-
-  RefPtr<MockWinWidget> mMockWinWidget;
-};
-
-TEST_F(WinInputPaneTest, HasNoEventHandlerAtCreation) {
-  HWND hwnd = CreateNativeWindow(/* aStyle = */ 0, /* aExStyle = */ 0);
-  ExpectHasEventHandler(hwnd, false);
-}
-
-TEST_F(WinInputPaneTest, HasEventHandlerAfterShowOnScreenKeyboard) {
-  HWND hwnd = CreateNativeWindow(/* aStyle = */ 0, /* aExStyle = */ 0);
-  ExpectHasEventHandler(hwnd, false);
-
-  OSKInputPaneManager::ShowOnScreenKeyboard(hwnd);
-  ExpectHasEventHandler(hwnd, true);
-}
diff --git a/widget/tests/gtest/moz.build b/widget/tests/gtest/moz.build
index 92b2c02f6b2f..613844fa781d 100644
--- a/widget/tests/gtest/moz.build
+++ b/widget/tests/gtest/moz.build
@@ -13,7 +13,6 @@ if CONFIG["OS_ARCH"] == "WINNT":
     UNIFIED_SOURCES += [
         "MockWinWidget.cpp",
         "TestWinHeaderOnlyUtils.cpp",
-        "TestWinInputPane.cpp",
         "TestWinMessageLoggingUtils.cpp",
         "TestWinWindowOcclusionTracker.cpp",
         "TestWinWindowOcclusionTrackerInteractive.cpp",
diff --git a/widget/windows/OSKInputPaneManager.cpp b/widget/windows/OSKInputPaneManager.cpp
index fa56eb241515..293a84cd28c8 100644
--- a/widget/windows/OSKInputPaneManager.cpp
+++ b/widget/windows/OSKInputPaneManager.cpp
@@ -7,17 +7,13 @@
 #define NTDDI_VERSION NTDDI_WIN10_RS1
 
 #include "OSKInputPaneManager.h"
-#include "mozilla/Maybe.h"
-#include "nscore.h"
 #include "nsDebug.h"
-#include "nsWindowsHelpers.h"
 
 #ifndef __MINGW32__
 #  include <inputpaneinterop.h>
 #  include <windows.ui.viewmanagement.h>
 #  include <wrl.h>
 
-using ABI::Windows::Foundation::ITypedEventHandler;
 using namespace ABI::Windows::UI::ViewManagement;
 using namespace Microsoft::WRL;
 using namespace Microsoft::WRL::Wrappers;
@@ -27,7 +23,7 @@ namespace mozilla {
 namespace widget {
 
 #ifndef __MINGW32__
-static ComPtr<IInputPane> GetInputPaneInternal(HWND aHwnd) {
+static ComPtr<IInputPane2> GetInputPane(HWND aHwnd) {
   ComPtr<IInputPaneInterop> inputPaneInterop;
   HRESULT hr = RoGetActivationFactory(
       HStringReference(RuntimeClass_Windows_UI_ViewManagement_InputPane).Get(),
@@ -42,44 +38,6 @@ static ComPtr<IInputPane> GetInputPaneInternal(HWND aHwnd) {
     return nullptr;
   }
 
-  return inputPane;
-}
-
-static ComPtr<IInputPane2> GetInputPane(HWND aHwnd) {
-  ComPtr<IInputPane> inputPane = GetInputPaneInternal(aHwnd);
-  if (!inputPane) {
-    return nullptr;
-  }
-
-  // Bug 1645571: We need to ensure that we have a SID_InputPaneEventHandler
-  // window service registered on aHwnd, or explorer.exe will mess with our
-  // window through twinui!CKeyboardOcclusionMitigation::_MitigateWindow.
-
-  Maybe<bool> hasEventHandler =
-      OSKInputPaneManager::HasInputPaneEventHandlerService(aHwnd);
-  if (hasEventHandler.isSome() && !hasEventHandler.value()) {
-    // Run IInputPane::add_Hiding once to register the window service.
-    EventRegistrationToken token{};
-    HRESULT registered = inputPane->add_Hiding(
-        Callback<ITypedEventHandler<InputPane*, InputPaneVisibilityEventArgs*>>(
-            [](IInputPane* aInputPane, IInputPaneVisibilityEventArgs* aArgs) {
-              return S_OK;
-            })
-            .Get(),
-        &token);
-
-    // Validate our assumption that we now have the window service registered.
-    hasEventHandler =
-        OSKInputPaneManager::HasInputPaneEventHandlerService(aHwnd);
-    if (SUCCEEDED(registered) &&
-        !(hasEventHandler.isSome() && hasEventHandler.value())) {
-      // If our assumption is wrong, we undo the operation. This prevents a
-      // memory leak where we would be adding a new callback every time the
-      // on-screen keyboard is shown.
-      inputPane->remove_Hiding(token);
-    }
-  }
-
   ComPtr<IInputPane2> inputPane2;
   inputPane.As(&inputPane2);
   return inputPane2;
@@ -139,42 +97,5 @@ void OSKInputPaneManager::DismissOnScreenKeyboard(HWND aWnd) {
 #endif
 }
 
-// static
-Maybe<bool> OSKInputPaneManager::HasInputPaneEventHandlerService(HWND aHwnd) {
-  using CoreIsWindowServiceSupportedFn =
-      HRESULT(WINAPI*)(HWND aHwnd, LPCGUID aServiceSid);
-
-  static auto sCoreIsWindowServiceSupported =
-      []() -> CoreIsWindowServiceSupportedFn {
-    HMODULE twinApiAppCore = LoadLibrarySystem32(L"twinapi.appcore.dll");
-    if (!twinApiAppCore) {
-      return nullptr;
-    }
-    return reinterpret_cast<CoreIsWindowServiceSupportedFn>(
-        ::GetProcAddress(twinApiAppCore, reinterpret_cast<LPCSTR>(8)));
-  }();
-
-  if (!sCoreIsWindowServiceSupported) {
-    return Nothing();
-  }
-
-  // {958e2b85-b035-4590-9bc5-ef01779b45dc}
-  static const GUID sSID_InputPaneEventHandler{
-      0x958e2b85,
-      0xb035,
-      0x4590,
-      {0x9b, 0xc5, 0xef, 0x1, 0x77, 0x9b, 0x45, 0xdc}};
-
-  // Since we are calling a Windows internal function here, the function
-  // signature is subject to arbitrary changes from Microsoft. This could
-  // result in wrong results or even crashing. Ensure that if things are so bad
-  // that we are about to crash, we just return Nothing instead.
-  MOZ_SEH_TRY {
-    return Some(SUCCEEDED(
-        sCoreIsWindowServiceSupported(aHwnd, &sSID_InputPaneEventHandler)));
-  }
-  MOZ_SEH_EXCEPT(EXCEPTION_EXECUTE_HANDLER) { return Nothing(); }
-}
-
 }  // namespace widget
 }  // namespace mozilla
diff --git a/widget/windows/OSKInputPaneManager.h b/widget/windows/OSKInputPaneManager.h
index 8224027cad2e..421a5f1e0291 100644
--- a/widget/windows/OSKInputPaneManager.h
+++ b/widget/windows/OSKInputPaneManager.h
@@ -7,8 +7,6 @@
 #ifndef mozilla_widget_OSKInputPaneManager_h
 #define mozilla_widget_OSKInputPaneManager_h
 
-#include "mozilla/Maybe.h"
-
 #include <windows.h>
 
 namespace mozilla {
@@ -18,7 +16,6 @@ class OSKInputPaneManager final {
  public:
   static void ShowOnScreenKeyboard(HWND aHwnd);
   static void DismissOnScreenKeyboard(HWND aHwnd);
-  static Maybe<bool> HasInputPaneEventHandlerService(HWND aHwnd);
 };
 
 }  // namespace widget
diff --git a/widget/windows/moz.build b/widget/windows/moz.build
index cbb66a5168fc..ea29a23239db 100644
--- a/widget/windows/moz.build
+++ b/widget/windows/moz.build
@@ -55,7 +55,6 @@ EXPORTS.mozilla.widget += [
     "InProcessWinCompositorWidget.h",
     "JumpListBuilder.h",
     "nsWindowLoggedMessages.h",
-    "OSKInputPaneManager.h",
     "WinCompositorWidget.h",
     "WinCompositorWindowThread.h",
     "WindowsEMF.h",