diff --git a/widget/cocoa/nsChildView.h b/widget/cocoa/nsChildView.h
index fe17d0d2a3d0..280ed6fd510f 100644
--- a/widget/cocoa/nsChildView.h
+++ b/widget/cocoa/nsChildView.h
@@ -288,9 +288,9 @@ class nsChildView final : public nsBaseWidget {
   nsChildView();
 
   // nsIWidget interface
-  virtual MOZ_MUST_USE nsresult Create(nsIWidget* aParent, nsNativeWidget aNativeParent,
-                                       const LayoutDeviceIntRect& aRect,
-                                       nsWidgetInitData* aInitData = nullptr) override;
+  [[nodiscard]] virtual nsresult Create(nsIWidget* aParent, nsNativeWidget aNativeParent,
+                                        const LayoutDeviceIntRect& aRect,
+                                        nsWidgetInitData* aInitData = nullptr) override;
 
   virtual void Destroy() override;
 
@@ -360,7 +360,7 @@ class nsChildView final : public nsBaseWidget {
 
   virtual nsresult SetTitle(const nsAString& title) override;
 
-  virtual MOZ_MUST_USE nsresult GetAttention(int32_t aCycleCount) override;
+  [[nodiscard]] virtual nsresult GetAttention(int32_t aCycleCount) override;
 
   virtual bool HasPendingInputEvent() override;
 
@@ -368,13 +368,14 @@ class nsChildView final : public nsBaseWidget {
   virtual void PostHandleKeyEvent(mozilla::WidgetKeyboardEvent* aEvent) override;
   virtual nsresult ActivateNativeMenuItemAt(const nsAString& indexString) override;
   virtual nsresult ForceUpdateNativeMenuAt(const nsAString& indexString) override;
-  virtual MOZ_MUST_USE nsresult GetSelectionAsPlaintext(nsAString& aResult) override;
+  [[nodiscard]] virtual nsresult GetSelectionAsPlaintext(nsAString& aResult) override;
 
   virtual void SetInputContext(const InputContext& aContext,
                                const InputContextAction& aAction) override;
   virtual InputContext GetInputContext() override;
   virtual TextEventDispatcherListener* GetNativeTextEventDispatcherListener() override;
-  virtual MOZ_MUST_USE nsresult AttachNativeKeyEvent(mozilla::WidgetKeyboardEvent& aEvent) override;
+  [[nodiscard]] virtual nsresult AttachNativeKeyEvent(
+      mozilla::WidgetKeyboardEvent& aEvent) override;
   virtual bool GetEditCommands(NativeKeyBindingsType aType,
                                const mozilla::WidgetKeyboardEvent& aEvent,
                                nsTArray<mozilla::CommandInt>& aCommands) override;
@@ -479,9 +480,9 @@ class nsChildView final : public nsBaseWidget {
     return nsCocoaUtils::DevPixelsToCocoaPoints(aRect, BackingScaleFactor());
   }
 
-  virtual MOZ_MUST_USE nsresult StartPluginIME(const mozilla::WidgetKeyboardEvent& aKeyboardEvent,
-                                               int32_t aPanelX, int32_t aPanelY,
-                                               nsString& aCommitted) override;
+  [[nodiscard]] virtual nsresult StartPluginIME(const mozilla::WidgetKeyboardEvent& aKeyboardEvent,
+                                                int32_t aPanelX, int32_t aPanelY,
+                                                nsString& aCommitted) override;
 
   virtual void SetPluginFocused(bool& aFocused) override;
 
diff --git a/widget/cocoa/nsCocoaWindow.h b/widget/cocoa/nsCocoaWindow.h
index 55611ed2c080..b983727f17f8 100644
--- a/widget/cocoa/nsCocoaWindow.h
+++ b/widget/cocoa/nsCocoaWindow.h
@@ -212,16 +212,18 @@ class nsCocoaWindow final : public nsBaseWidget, public nsPIWidgetCocoa {
  public:
   nsCocoaWindow();
 
+  // clang-format off
   NS_DECL_ISUPPORTS_INHERITED
   NS_DECL_NSPIWIDGETCOCOA
 
-  virtual MOZ_MUST_USE nsresult Create(nsIWidget* aParent, nsNativeWidget aNativeParent,
-                                       const DesktopIntRect& aRect,
-                                       nsWidgetInitData* aInitData = nullptr) override;
+  [[nodiscard]] virtual nsresult Create(nsIWidget* aParent, nsNativeWidget aNativeParent,
+                                        const DesktopIntRect& aRect,
+                                        nsWidgetInitData* aInitData = nullptr) override;
+  // clang-format on
 
-  virtual MOZ_MUST_USE nsresult Create(nsIWidget* aParent, nsNativeWidget aNativeParent,
-                                       const LayoutDeviceIntRect& aRect,
-                                       nsWidgetInitData* aInitData = nullptr) override;
+  [[nodiscard]] virtual nsresult Create(nsIWidget* aParent, nsNativeWidget aNativeParent,
+                                        const LayoutDeviceIntRect& aRect,
+                                        nsWidgetInitData* aInitData = nullptr) override;
 
   virtual void Destroy() override;
 
@@ -293,7 +295,7 @@ class nsCocoaWindow final : public nsBaseWidget, public nsPIWidgetCocoa {
       LayerManagerPersistence aPersistence = LAYER_MANAGER_CURRENT) override;
   virtual nsresult DispatchEvent(mozilla::WidgetGUIEvent* aEvent, nsEventStatus& aStatus) override;
   virtual void CaptureRollupEvents(nsIRollupListener* aListener, bool aDoCapture) override;
-  virtual MOZ_MUST_USE nsresult GetAttention(int32_t aCycleCount) override;
+  [[nodiscard]] virtual nsresult GetAttention(int32_t aCycleCount) override;
   virtual bool HasPendingInputEvent() override;
   virtual nsTransparencyMode GetTransparencyMode() override;
   virtual void SetTransparencyMode(nsTransparencyMode aMode) override;
diff --git a/widget/cocoa/nsNativeThemeCocoa.h b/widget/cocoa/nsNativeThemeCocoa.h
index bae09d645ec7..ddab034f3d86 100644
--- a/widget/cocoa/nsNativeThemeCocoa.h
+++ b/widget/cocoa/nsNativeThemeCocoa.h
@@ -398,8 +398,8 @@ class nsNativeThemeCocoa : private nsNativeTheme, public nsITheme {
                                         mozilla::layers::RenderRootStateManager* aManager,
                                         nsIFrame* aFrame, StyleAppearance aAppearance,
                                         const nsRect& aRect) override;
-  MOZ_MUST_USE LayoutDeviceIntMargin GetWidgetBorder(nsDeviceContext* aContext, nsIFrame* aFrame,
-                                                     StyleAppearance aAppearance) override;
+  [[nodiscard]] LayoutDeviceIntMargin GetWidgetBorder(nsDeviceContext* aContext, nsIFrame* aFrame,
+                                                      StyleAppearance aAppearance) override;
 
   bool GetWidgetPadding(nsDeviceContext* aContext, nsIFrame* aFrame, StyleAppearance aAppearance,
                         LayoutDeviceIntMargin* aResult) override;
diff --git a/widget/uikit/nsWindow.h b/widget/uikit/nsWindow.h
index a162274794d2..60454586de31 100644
--- a/widget/uikit/nsWindow.h
+++ b/widget/uikit/nsWindow.h
@@ -27,9 +27,9 @@ class nsWindow final : public nsBaseWidget {
   // nsIWidget
   //
 
-  virtual MOZ_MUST_USE nsresult Create(nsIWidget* aParent, nsNativeWidget aNativeParent,
-                                       const LayoutDeviceIntRect& aRect,
-                                       nsWidgetInitData* aInitData = nullptr) override;
+  [[nodiscard]] virtual nsresult
+      Create(nsIWidget* aParent, nsNativeWidget aNativeParent, const LayoutDeviceIntRect& aRect,
+             nsWidgetInitData* aInitData = nullptr) override;
   virtual void Destroy() override;
   virtual void Show(bool aState) override;
   virtual void Enable(bool aState) override {}