--- a/widget/windows/WinUtils.cpp
+++ b/widget/windows/WinUtils.cpp
@@ -470,17 +470,17 @@ WinUtils::Initialize()
 #endif
 }
 
 // static
 LRESULT WINAPI
 WinUtils::NonClientDpiScalingDefWindowProcW(HWND hWnd, UINT msg,
                                             WPARAM wParam, LPARAM lParam)
 {
-  if (msg == WM_NCCREATE) {
+  if (msg == WM_NCCREATE && sEnableNonClientDpiScaling) {
     sEnableNonClientDpiScaling(hWnd);
   }
   return ::DefWindowProcW(hWnd, msg, wParam, lParam);
 }
 
 // static
 void
 WinUtils::LogW(const wchar_t *fmt, ...)

--- a/widget/windows/WinUtils.h
+++ b/widget/windows/WinUtils.h
@@ -158,22 +158,16 @@ public:
 
 class WinUtils
 {
   // Function pointers for APIs that may not be available depending on
   // the Win10 update version -- will be set up in Initialize().
   static SetThreadDpiAwarenessContextProc sSetThreadDpiAwarenessContext;
   static EnableNonClientDpiScalingProc sEnableNonClientDpiScaling;
 
-  // Wrapper for DefWindowProc that will enable non-client dpi scaling on the
-  // window during creation.
-  static LRESULT WINAPI
-  NonClientDpiScalingDefWindowProcW(HWND hWnd, UINT msg,
-                                    WPARAM wParam, LPARAM lParam);
-
 public:
   class AutoSystemDpiAware
   {
   public:
     AutoSystemDpiAware()
     {
       if (sSetThreadDpiAwarenessContext) {
         mPrevContext = sSetThreadDpiAwarenessContext(DPI_AWARENESS_CONTEXT_SYSTEM_AWARE);
@@ -186,21 +180,21 @@ public:
         sSetThreadDpiAwarenessContext(mPrevContext);
       }
     }
 
   private:
     DPI_AWARENESS_CONTEXT mPrevContext;
   };
 
-  static decltype(::DefWindowProcW)* GetDefWindowProc()
-  {
-    return sEnableNonClientDpiScaling ? NonClientDpiScalingDefWindowProcW :
-                                        ::DefWindowProcW;
-  }
+  // Wrapper for DefWindowProc that will enable non-client dpi scaling on the
+  // window during creation.
+  static LRESULT WINAPI
+  NonClientDpiScalingDefWindowProcW(HWND hWnd, UINT msg,
+                                    WPARAM wParam, LPARAM lParam);
 
   /**
    * Get the system's default logical-to-physical DPI scaling factor,
    * which is based on the primary display. Note however that unlike
    * LogToPhysFactor(GetPrimaryMonitor()), this will not change during
    * a session even if the displays are reconfigured. This scale factor
    * is used by Windows theme metrics etc, which do not fully support
    * dynamic resolution changes but are only updated on logout.

--- a/widget/windows/nsWindow.cpp
+++ b/widget/windows/nsWindow.cpp
@@ -1010,17 +1010,17 @@ nsWindow::RegisterWindowClass(const wcha
 {
   WNDCLASSW wc;
   if (::GetClassInfoW(nsToolkit::mDllInstance, aClassName, &wc)) {
     // already registered
     return aClassName;
   }
 
   wc.style         = CS_DBLCLKS | aExtraStyle;
-  wc.lpfnWndProc   = WinUtils::GetDefWindowProc();
+  wc.lpfnWndProc   = WinUtils::NonClientDpiScalingDefWindowProcW;
   wc.cbClsExtra    = 0;
   wc.cbWndExtra    = 0;
   wc.hInstance     = nsToolkit::mDllInstance;
   wc.hIcon         = aIconID ? ::LoadIconW(::GetModuleHandleW(nullptr), aIconID) : nullptr;
   wc.hCursor       = nullptr;
   wc.hbrBackground = mBrush;
   wc.lpszMenuName  = nullptr;
   wc.lpszClassName = aClassName;