diff --git a/widget/android/nsWindow.h b/widget/android/nsWindow.h
index e3a926c40cb7..49051bd47623 100644
--- a/widget/android/nsWindow.h
+++ b/widget/android/nsWindow.h
@@ -41,7 +41,7 @@ namespace mozilla {
     } // namespace ipc
 }
 
-class nsWindow : public nsBaseWidget
+class nsWindow final : public nsBaseWidget
 {
 private:
     virtual ~nsWindow();
diff --git a/widget/gtk/nsWidgetFactory.cpp b/widget/gtk/nsWidgetFactory.cpp
index e01523114e18..3c8bc02ebbb5 100644
--- a/widget/gtk/nsWidgetFactory.cpp
+++ b/widget/gtk/nsWidgetFactory.cpp
@@ -66,7 +66,6 @@ using namespace mozilla::widget;
 static NS_DEFINE_CID(kXULFilePickerCID, XULFILEPICKER_CID);
 
 NS_GENERIC_FACTORY_CONSTRUCTOR(nsWindow)
-NS_GENERIC_FACTORY_CONSTRUCTOR(nsChildWindow)
 NS_GENERIC_FACTORY_CONSTRUCTOR(nsTransferable)
 NS_GENERIC_FACTORY_CONSTRUCTOR(nsBidiKeyboard)
 NS_GENERIC_FACTORY_CONSTRUCTOR(nsHTMLFormatConverter)
@@ -230,7 +229,7 @@ NS_DEFINE_NAMED_CID(NS_GFXINFO_CID);
 
 static const mozilla::Module::CIDEntry kWidgetCIDs[] = {
     { &kNS_WINDOW_CID, false, nullptr, nsWindowConstructor },
-    { &kNS_CHILD_CID, false, nullptr, nsChildWindowConstructor },
+    { &kNS_CHILD_CID, false, nullptr, nsWindowConstructor },
     { &kNS_APPSHELL_CID, false, nullptr, nsAppShellConstructor, Module::ALLOW_IN_GPU_PROCESS },
     { &kNS_COLORPICKER_CID, false, nullptr, nsColorPickerConstructor, Module::MAIN_PROCESS_ONLY },
     { &kNS_FILEPICKER_CID, false, nullptr, nsFilePickerConstructor, Module::MAIN_PROCESS_ONLY },
diff --git a/widget/gtk/nsWindow.cpp b/widget/gtk/nsWindow.cpp
index c2316f45be7a..d9629ff50658 100644
--- a/widget/gtk/nsWindow.cpp
+++ b/widget/gtk/nsWindow.cpp
@@ -6192,12 +6192,6 @@ nsWindow::DispatchRestoreEventAccessible(void)
 
 #endif /* #ifdef ACCESSIBILITY */
 
-// nsChildWindow class
-
-nsChildWindow::nsChildWindow() = default;
-
-nsChildWindow::~nsChildWindow() = default;
-
 void
 nsWindow::SetInputContext(const InputContext& aContext,
                           const InputContextAction& aAction)
diff --git a/widget/gtk/nsWindow.h b/widget/gtk/nsWindow.h
index 6ecfc52fdd9c..55b37ce15421 100644
--- a/widget/gtk/nsWindow.h
+++ b/widget/gtk/nsWindow.h
@@ -68,7 +68,7 @@ class TimeStamp;
 class CurrentX11TimeGetter;
 }
 
-class nsWindow : public nsBaseWidget
+class nsWindow final : public nsBaseWidget
 {
 public:
     typedef mozilla::gfx::DrawTarget DrawTarget;
@@ -567,10 +567,4 @@ private:
     mozilla::UniquePtr<mozilla::CurrentX11TimeGetter> mCurrentTimeGetter;
 };
 
-class nsChildWindow : public nsWindow {
-public:
-    nsChildWindow();
-    ~nsChildWindow();
-};
-
 #endif /* __nsWindow_h__ */
diff --git a/widget/uikit/nsWindow.h b/widget/uikit/nsWindow.h
index 801b889f58a6..48a20ddf699c 100644
--- a/widget/uikit/nsWindow.h
+++ b/widget/uikit/nsWindow.h
@@ -15,7 +15,7 @@
 @class UIView;
 @class ChildView;
 
-class nsWindow :
+class nsWindow final :
     public nsBaseWidget
 {
     typedef nsBaseWidget Inherited;