--- a/gfx/thebes/gfxFont.h
+++ b/gfx/thebes/gfxFont.h
@@ -2937,20 +2937,20 @@ public:
         gfxFloat mPartWidth;
         
         bool mClipBeforePart;
         bool mClipAfterPart;
     };
     
     // return storage used by this run, for memory reporter;
     // nsTransformedTextRun needs to override this as it holds additional data
-    virtual NS_MUST_OVERRIDE size_t
-        SizeOfExcludingThis(nsMallocSizeOfFun aMallocSizeOf);
-    virtual NS_MUST_OVERRIDE size_t
-        SizeOfIncludingThis(nsMallocSizeOfFun aMallocSizeOf);
+    virtual size_t SizeOfExcludingThis(nsMallocSizeOfFun aMallocSizeOf)
+      MOZ_MUST_OVERRIDE;
+    virtual size_t SizeOfIncludingThis(nsMallocSizeOfFun aMallocSizeOf)
+      MOZ_MUST_OVERRIDE;
 
     // Get the size, if it hasn't already been gotten, marking as it goes.
     size_t MaybeSizeOfIncludingThis(nsMallocSizeOfFun aMallocSizeOf)  {
         if (mFlags & gfxTextRunFactory::TEXT_RUN_SIZE_ACCOUNTED) {
             return 0;
         }
         mFlags |= gfxTextRunFactory::TEXT_RUN_SIZE_ACCOUNTED;
         return SizeOfIncludingThis(aMallocSizeOf);

--- a/layout/generic/nsFrame.h
+++ b/layout/generic/nsFrame.h
@@ -82,18 +82,18 @@
 
 // Frame allocation boilerplate macros.  Every subclass of nsFrame
 // must define its own operator new and GetAllocatedSize.  If they do
 // not, the per-frame recycler lists in nsPresArena will not work
 // correctly, with potentially catastrophic consequences (not enough
 // memory is allocated for a frame object).
 
 #define NS_DECL_FRAMEARENA_HELPERS                                \
-  NS_MUST_OVERRIDE void* operator new(size_t, nsIPresShell*);     \
-  virtual NS_MUST_OVERRIDE nsQueryFrame::FrameIID GetFrameId();
+  void* operator new(size_t, nsIPresShell*) MOZ_MUST_OVERRIDE;    \
+  virtual nsQueryFrame::FrameIID GetFrameId() MOZ_MUST_OVERRIDE;
 
 #define NS_IMPL_FRAMEARENA_HELPERS(class)                         \
   void* class::operator new(size_t sz, nsIPresShell* aShell)      \
   { return aShell->AllocateFrame(nsQueryFrame::class##_id, sz); } \
   nsQueryFrame::FrameIID class::GetFrameId()                      \
   { return nsQueryFrame::class##_id; }
 
 //----------------------------------------------------------------------

--- a/layout/generic/nsTextRunTransformations.h
+++ b/layout/generic/nsTextRunTransformations.h
@@ -97,18 +97,18 @@ public:
   {
     if (mNeedsRebuild) {
       mNeedsRebuild = false;
       mFactory->RebuildTextRun(this, aRefContext);
     }
   }
 
   // override the gfxTextRun impls to account for additional members here
-  virtual NS_MUST_OVERRIDE size_t SizeOfExcludingThis(nsMallocSizeOfFun aMallocSizeOf);
-  virtual NS_MUST_OVERRIDE size_t SizeOfIncludingThis(nsMallocSizeOfFun aMallocSizeOf);
+  virtual size_t SizeOfExcludingThis(nsMallocSizeOfFun aMallocSizeOf) MOZ_MUST_OVERRIDE;
+  virtual size_t SizeOfIncludingThis(nsMallocSizeOfFun aMallocSizeOf) MOZ_MUST_OVERRIDE;
 
   nsTransformingTextRunFactory       *mFactory;
   nsTArray<nsRefPtr<nsStyleContext> > mStyles;
   nsTArray<bool>                      mCapitalize;
   nsString                            mString;
   bool                                mOwnsFactory;
   bool                                mNeedsRebuild;
 

--- a/layout/style/AnimationCommon.h
+++ b/layout/style/AnimationCommon.h
@@ -37,20 +37,20 @@ public:
   NS_DECL_ISUPPORTS
 
   // nsIStyleRuleProcessor (parts)
   virtual nsRestyleHint HasStateDependentStyle(StateRuleProcessorData* aData);
   virtual bool HasDocumentStateDependentStyle(StateRuleProcessorData* aData) MOZ_OVERRIDE;
   virtual nsRestyleHint
     HasAttributeDependentStyle(AttributeRuleProcessorData* aData) MOZ_OVERRIDE;
   virtual bool MediumFeaturesChanged(nsPresContext* aPresContext) MOZ_OVERRIDE;
-  virtual NS_MUST_OVERRIDE size_t
-    SizeOfExcludingThis(nsMallocSizeOfFun aMallocSizeOf) const MOZ_OVERRIDE;
-  virtual NS_MUST_OVERRIDE size_t
-    SizeOfIncludingThis(nsMallocSizeOfFun aMallocSizeOf) const MOZ_OVERRIDE;
+  virtual size_t SizeOfExcludingThis(nsMallocSizeOfFun aMallocSizeOf)
+    const MOZ_MUST_OVERRIDE MOZ_OVERRIDE;
+  virtual size_t SizeOfIncludingThis(nsMallocSizeOfFun aMallocSizeOf)
+    const MOZ_MUST_OVERRIDE MOZ_OVERRIDE;
 
   /**
    * Notify the manager that the pres context is going away.
    */
   void Disconnect();
 
   enum FlushFlags {
     Can_Throttle,

--- a/layout/style/GroupRule.h
+++ b/layout/style/GroupRule.h
@@ -62,20 +62,19 @@ public:
    */
   nsresult DeleteStyleRuleAt(uint32_t aIndex);
   nsresult InsertStyleRuleAt(uint32_t aIndex, Rule* aRule);
   nsresult ReplaceStyleRule(Rule *aOld, Rule *aNew);
 
   virtual bool UseForPresentation(nsPresContext* aPresContext,
                                     nsMediaQueryResultCacheKey& aKey) = 0;
 
-  NS_MUST_OVERRIDE size_t   // non-virtual -- it is only called by subclasses
-    SizeOfExcludingThis(nsMallocSizeOfFun aMallocSizeOf) const;
-  virtual size_t
-    SizeOfIncludingThis(nsMallocSizeOfFun aMallocSizeOf) const = 0;
+  // non-virtual -- it is only called by subclasses
+  size_t SizeOfExcludingThis(nsMallocSizeOfFun aMallocSizeOf) const;
+  virtual size_t SizeOfIncludingThis(nsMallocSizeOfFun aMallocSizeOf) const = 0;
 
 protected:
   // to help implement nsIDOMCSSRule
   nsresult AppendRulesToCssText(nsAString& aCssText);
 
   // to implement common methods on nsIDOMCSSMediaRule and
   // nsIDOMCSSMozDocumentRule
   nsresult GetCssRules(nsIDOMCSSRuleList* *aRuleList);

--- a/layout/style/NameSpaceRule.h
+++ b/layout/style/NameSpaceRule.h
@@ -47,18 +47,18 @@ public:
   // Rule methods
   virtual int32_t GetType() const;
   virtual already_AddRefed<Rule> Clone() const;
 
   nsIAtom* GetPrefix() const { return mPrefix; }
 
   void GetURLSpec(nsString& aURLSpec) const { aURLSpec = mURLSpec; }
 
-  virtual NS_MUST_OVERRIDE size_t
-    SizeOfIncludingThis(nsMallocSizeOfFun aMallocSizeOf) const;
+  virtual size_t SizeOfIncludingThis(nsMallocSizeOfFun aMallocSizeOf) const
+    MOZ_MUST_OVERRIDE;
 
   // nsIDOMCSSRule interface
   NS_DECL_NSIDOMCSSRULE
 
 private:
   nsCOMPtr<nsIAtom> mPrefix;
   nsString          mURLSpec;
 };

--- a/layout/style/Rule.h
+++ b/layout/style/Rule.h
@@ -105,18 +105,18 @@ public:
   virtual nsIDOMCSSRule* GetExistingDOMRule() = 0;
 
   // to implement methods on nsIDOMCSSRule
   nsresult GetParentRule(nsIDOMCSSRule** aParentRule);
   nsresult GetParentStyleSheet(nsIDOMCSSStyleSheet** aSheet);
 
   // This is pure virtual because all of Rule's data members are non-owning and
   // thus measured elsewhere.
-  virtual NS_MUST_OVERRIDE size_t
-    SizeOfIncludingThis(nsMallocSizeOfFun aMallocSizeOf) const = 0;
+  virtual size_t SizeOfIncludingThis(nsMallocSizeOfFun aMallocSizeOf)
+    const MOZ_MUST_OVERRIDE = 0;
 
   // This is used to measure nsCOMArray<Rule>s.
   static size_t SizeOfCOMArrayElementIncludingThis(css::Rule* aElement,
                                                    nsMallocSizeOfFun aMallocSizeOf,
                                                    void* aData);
 
 protected:
   // This is either an nsCSSStyleSheet* or a nsHTMLStyleSheet*.  The former

--- a/layout/style/nsAnimationManager.h
+++ b/layout/style/nsAnimationManager.h
@@ -217,20 +217,20 @@ public:
 
   // nsIStyleRuleProcessor (parts)
   virtual void RulesMatching(ElementRuleProcessorData* aData) MOZ_OVERRIDE;
   virtual void RulesMatching(PseudoElementRuleProcessorData* aData) MOZ_OVERRIDE;
   virtual void RulesMatching(AnonBoxRuleProcessorData* aData) MOZ_OVERRIDE;
 #ifdef MOZ_XUL
   virtual void RulesMatching(XULTreeRuleProcessorData* aData) MOZ_OVERRIDE;
 #endif
-  virtual NS_MUST_OVERRIDE size_t
-    SizeOfExcludingThis(nsMallocSizeOfFun aMallocSizeOf) const MOZ_OVERRIDE;
-  virtual NS_MUST_OVERRIDE size_t
-    SizeOfIncludingThis(nsMallocSizeOfFun aMallocSizeOf) const MOZ_OVERRIDE;
+  virtual size_t SizeOfExcludingThis(nsMallocSizeOfFun aMallocSizeOf)
+    const MOZ_MUST_OVERRIDE MOZ_OVERRIDE;
+  virtual size_t SizeOfIncludingThis(nsMallocSizeOfFun aMallocSizeOf)
+    const MOZ_MUST_OVERRIDE MOZ_OVERRIDE;
 
   // nsARefreshObserver
   virtual void WillRefresh(mozilla::TimeStamp aTime) MOZ_OVERRIDE;
 
   void FlushAnimations(FlushFlags aFlags);
 
   /**
    * Return the style rule that RulesMatching should add for

--- a/layout/style/nsCSSRuleProcessor.h
+++ b/layout/style/nsCSSRuleProcessor.h
@@ -107,20 +107,20 @@ public:
 
   virtual bool HasDocumentStateDependentStyle(StateRuleProcessorData* aData) MOZ_OVERRIDE;
 
   virtual nsRestyleHint
     HasAttributeDependentStyle(AttributeRuleProcessorData* aData) MOZ_OVERRIDE;
 
   virtual bool MediumFeaturesChanged(nsPresContext* aPresContext) MOZ_OVERRIDE;
 
-  virtual NS_MUST_OVERRIDE size_t
-    SizeOfExcludingThis(nsMallocSizeOfFun mallocSizeOf) const MOZ_OVERRIDE;
-  virtual NS_MUST_OVERRIDE size_t
-    SizeOfIncludingThis(nsMallocSizeOfFun mallocSizeOf) const MOZ_OVERRIDE;
+  virtual size_t SizeOfExcludingThis(nsMallocSizeOfFun mallocSizeOf)
+    const MOZ_MUST_OVERRIDE MOZ_OVERRIDE;
+  virtual size_t SizeOfIncludingThis(nsMallocSizeOfFun mallocSizeOf)
+    const MOZ_MUST_OVERRIDE MOZ_OVERRIDE;
 
   // Append all the currently-active font face rules to aArray.  Return
   // true for success and false for failure.
   bool AppendFontFaceRules(nsPresContext* aPresContext,
                            nsTArray<nsFontFaceRuleContainer>& aArray);
 
   bool AppendKeyframesRules(nsPresContext* aPresContext,
                             nsTArray<nsCSSKeyframesRule*>& aArray);

--- a/layout/style/nsCSSRules.h
+++ b/layout/style/nsCSSRules.h
@@ -84,18 +84,18 @@ public:
 
   // rest of GroupRule
   virtual bool UseForPresentation(nsPresContext* aPresContext,
                                     nsMediaQueryResultCacheKey& aKey);
 
   // @media rule methods
   nsresult SetMedia(nsMediaList* aMedia);
   
-  virtual NS_MUST_OVERRIDE size_t
-    SizeOfIncludingThis(nsMallocSizeOfFun aMallocSizeOf) const;
+  virtual size_t SizeOfIncludingThis(nsMallocSizeOfFun aMallocSizeOf)
+    const MOZ_MUST_OVERRIDE;
 
 protected:
   void AppendConditionText(nsAString& aOutput);
 
   nsRefPtr<nsMediaList> mMedia;
 };
 
 class DocumentRule MOZ_FINAL : public GroupRule,
@@ -162,18 +162,18 @@ public:
       , next(aOther.next ? new URL(*aOther.next) : nullptr)
     {
     }
     ~URL();
   };
 
   void SetURLs(URL *aURLs) { mURLs = aURLs; }
 
-  virtual NS_MUST_OVERRIDE size_t
-    SizeOfIncludingThis(nsMallocSizeOfFun aMallocSizeOf) const;
+  virtual size_t SizeOfIncludingThis(nsMallocSizeOfFun aMallocSizeOf)
+    const MOZ_MUST_OVERRIDE;
 
 protected:
   void AppendConditionText(nsAString& aOutput);
 
   nsAutoPtr<URL> mURLs; // linked list of |struct URL| above.
 };
 
 } // namespace css

--- a/layout/style/nsHTMLCSSStyleSheet.h
+++ b/layout/style/nsHTMLCSSStyleSheet.h
@@ -54,20 +54,20 @@ public:
 #ifdef MOZ_XUL
   virtual void RulesMatching(XULTreeRuleProcessorData* aData) MOZ_OVERRIDE;
 #endif
   virtual nsRestyleHint HasStateDependentStyle(StateRuleProcessorData* aData) MOZ_OVERRIDE;
   virtual bool HasDocumentStateDependentStyle(StateRuleProcessorData* aData) MOZ_OVERRIDE;
   virtual nsRestyleHint
     HasAttributeDependentStyle(AttributeRuleProcessorData* aData) MOZ_OVERRIDE;
   virtual bool MediumFeaturesChanged(nsPresContext* aPresContext) MOZ_OVERRIDE;
-  virtual NS_MUST_OVERRIDE size_t
-    SizeOfExcludingThis(nsMallocSizeOfFun aMallocSizeOf) const MOZ_OVERRIDE;
-  virtual NS_MUST_OVERRIDE size_t
-    SizeOfIncludingThis(nsMallocSizeOfFun aMallocSizeOf) const MOZ_OVERRIDE;
+  virtual size_t SizeOfExcludingThis(nsMallocSizeOfFun aMallocSizeOf)
+    const MOZ_MUST_OVERRIDE MOZ_OVERRIDE;
+  virtual size_t SizeOfIncludingThis(nsMallocSizeOfFun aMallocSizeOf)
+    const MOZ_MUST_OVERRIDE MOZ_OVERRIDE;
 
   void CacheStyleAttr(const nsAString& aSerialized, MiscContainer* aValue);
   void EvictStyleAttr(const nsAString& aSerialized, MiscContainer* aValue);
   MiscContainer* LookupStyleAttr(const nsAString& aSerialized);
 
 private: 
   nsHTMLCSSStyleSheet(const nsHTMLCSSStyleSheet& aCopy) MOZ_DELETE;
   nsHTMLCSSStyleSheet& operator=(const nsHTMLCSSStyleSheet& aCopy) MOZ_DELETE;

--- a/layout/style/nsHTMLStyleSheet.h
+++ b/layout/style/nsHTMLStyleSheet.h
@@ -55,20 +55,20 @@ public:
 #ifdef MOZ_XUL
   virtual void RulesMatching(XULTreeRuleProcessorData* aData) MOZ_OVERRIDE;
 #endif
   virtual nsRestyleHint HasStateDependentStyle(StateRuleProcessorData* aData) MOZ_OVERRIDE;
   virtual bool HasDocumentStateDependentStyle(StateRuleProcessorData* aData) MOZ_OVERRIDE;
   virtual nsRestyleHint
     HasAttributeDependentStyle(AttributeRuleProcessorData* aData) MOZ_OVERRIDE;
   virtual bool MediumFeaturesChanged(nsPresContext* aPresContext) MOZ_OVERRIDE;
-  virtual NS_MUST_OVERRIDE size_t
-    SizeOfExcludingThis(nsMallocSizeOfFun aMallocSizeOf) const MOZ_OVERRIDE;
-  virtual NS_MUST_OVERRIDE size_t
-    SizeOfIncludingThis(nsMallocSizeOfFun aMallocSizeOf) const MOZ_OVERRIDE;
+  virtual size_t SizeOfExcludingThis(nsMallocSizeOfFun aMallocSizeOf)
+    const MOZ_MUST_OVERRIDE MOZ_OVERRIDE;
+  virtual size_t SizeOfIncludingThis(nsMallocSizeOfFun aMallocSizeOf)
+    const MOZ_MUST_OVERRIDE MOZ_OVERRIDE;
   size_t DOMSizeOfIncludingThis(nsMallocSizeOfFun aMallocSizeOf) const;
 
   void Reset(nsIURI* aURL);
   nsresult SetLinkColor(nscolor aColor);
   nsresult SetActiveLinkColor(nscolor aColor);
   nsresult SetVisitedLinkColor(nscolor aColor);
 
   // Mapped Attribute management methods

--- a/layout/style/nsTransitionManager.h
+++ b/layout/style/nsTransitionManager.h
@@ -165,20 +165,20 @@ public:
 
   // nsIStyleRuleProcessor (parts)
   virtual void RulesMatching(ElementRuleProcessorData* aData) MOZ_OVERRIDE;
   virtual void RulesMatching(PseudoElementRuleProcessorData* aData) MOZ_OVERRIDE;
   virtual void RulesMatching(AnonBoxRuleProcessorData* aData) MOZ_OVERRIDE;
 #ifdef MOZ_XUL
   virtual void RulesMatching(XULTreeRuleProcessorData* aData) MOZ_OVERRIDE;
 #endif
-  virtual NS_MUST_OVERRIDE size_t
-    SizeOfExcludingThis(nsMallocSizeOfFun aMallocSizeOf) const MOZ_OVERRIDE;
-  virtual NS_MUST_OVERRIDE size_t
-    SizeOfIncludingThis(nsMallocSizeOfFun aMallocSizeOf) const MOZ_OVERRIDE;
+  virtual size_t SizeOfExcludingThis(nsMallocSizeOfFun aMallocSizeOf) const
+    MOZ_MUST_OVERRIDE MOZ_OVERRIDE;
+  virtual size_t SizeOfIncludingThis(nsMallocSizeOfFun aMallocSizeOf) const
+    MOZ_MUST_OVERRIDE MOZ_OVERRIDE;
 
   // nsARefreshObserver
   virtual void WillRefresh(mozilla::TimeStamp aTime) MOZ_OVERRIDE;
 
   void FlushTransitions(FlushFlags aFlags);
 
   // Performs a 'mini-flush' to make styles from throttled transitions
   // up-to-date prior to processing an unrelated style change, so that

--- a/mfbt/Attributes.h
+++ b/mfbt/Attributes.h
@@ -314,11 +314,69 @@
  *   MOZ_WARN_UNUSED_RESULT int foo() { return 42; }
  */
 #if defined(__GNUC__) || defined(__clang__)
 #  define MOZ_WARN_UNUSED_RESULT __attribute__ ((warn_unused_result))
 #else
 #  define MOZ_WARN_UNUSED_RESULT
 #endif
 
+/*
+ * The following macros are attributes that support the static analysis plugin
+ * included with Mozilla, and will be implemented (when such support is enabled)
+ * as C++11 attributes. Since such attributes are legal pretty much everywhere
+ * and have subtly different semantics depending on their placement, the
+ * following is a guide on where to place the attributes.
+ *
+ * Attributes that apply to a struct or class precede the name of the class:
+ * (Note that this is different from the placement of MOZ_FINAL for classes!)
+ *
+ *   class MOZ_CLASS_ATTRIBUTE SomeClass {};
+ *
+ * Attributes that apply to functions follow the parentheses and const
+ * qualifiers but precede MOZ_FINAL, MOZ_OVERRIDE and the function body:
+ *
+ *   void DeclaredFunction() MOZ_FUNCTION_ATTRIBUTE;
+ *   void SomeFunction() MOZ_FUNCTION_ATTRIBUTE {}
+ *   void PureFunction() const MOZ_FUNCTION_ATTRIBUTE = 0;
+ *   void OverriddenFunction() MOZ_FUNCTION_ATTIRBUTE MOZ_OVERRIDE;
+ *
+ * Attributes that apply to variables or parameters follow the variable's name:
+ *
+ *   int variable MOZ_VARIABLE_ATTRIBUTE;
+ *
+ * Attributes that apply to types follow the type name:
+ *
+ *   typedef int MOZ_TYPE_ATTRIBUTE MagicInt;
+ *   int MOZ_TYPE_ATTRIBUTE someVariable;
+ *   int * MOZ_TYPE_ATTRIBUTE magicPtrInt;
+ *   int MOZ_TYPE_ATTRIBUTE * ptrToMagicInt;
+ *
+ * Attributes that apply to statements precede the statement:
+ *
+ *   MOZ_IF_ATTRIBUTE if (x == 0)
+ *   MOZ_DO_ATTRIBUTE do { } while(0);
+ *
+ * Attributes that apply to labels precede the label:
+ *
+ *   MOZ_LABEL_ATTRIBUTE target:
+ *     goto target;
+ *   MOZ_CASE_ATTRIBUTE case 5:
+ *   MOZ_DEFAULT_ATTRIBUTE default:
+ *
+ * The static analyses that are performed by the plugin are as follows:
+ *
+ * MOZ_MUST_OVERRIDE: Applies to all C++ member functions. All immediate
+ *   subclasses must provide an exact override of this method; if a subclass
+ *   does not override this method, the compiler will emit an error. This
+ *   attribute is not limited to virtual methods, so if it is applied to a
+ *   nonvirtual method and the subclass does not provide an equivalent
+ *   definition, the compiler will emit an error.
+ */
+#ifdef MOZ_CLANG_PLUGIN
+# define MOZ_MUST_OVERRIDE __attribute__((annotate("moz_must_override")))
+#else
+# define MOZ_MUST_OVERRIDE /* nothing */
+#endif /* MOZ_CLANG_PLUGIN */
+
 #endif /* __cplusplus */
 
 #endif  /* mozilla_Attributes_h_ */

--- a/xpcom/base/nscore.h
+++ b/xpcom/base/nscore.h
@@ -372,38 +372,25 @@ typedef uint32_t nsrefcnt;
 #if defined(HAVE_THREAD_TLS_KEYWORD)
 #define NS_TLS __thread
 #endif
 
 /**
  * Static type annotations, enforced when static-checking is enabled:
  *
  * NS_STACK_CLASS: a class which must only be instantiated on the stack
- *
- * NS_MUST_OVERRIDE:
- *   a method which every immediate subclass of this class must
- *   override.  A subclass override can itself be NS_MUST_OVERRIDE, in
- *   which case its own subclasses must override the method as well.
- *
- *   This is similar to, but not the same as, marking a method pure
- *   virtual.  It has no effect on the class in which the annotation
- *   appears, you can still provide a definition for the method, and
- *   it objects to the mere existence of a subclass that doesn't
- *   override the method.  See examples in analysis/must-override.js.
  */
 #ifdef NS_STATIC_CHECKING
 #define NS_STACK_CLASS __attribute__((user("NS_stack")))
 #define NS_OKONHEAP    __attribute__((user("NS_okonheap")))
 #define NS_SUPPRESS_STACK_CHECK __attribute__((user("NS_suppress_stackcheck")))
-#define NS_MUST_OVERRIDE __attribute__((user("NS_must_override")))
 #else
 #define NS_STACK_CLASS
 #define NS_OKONHEAP
 #define NS_SUPPRESS_STACK_CHECK
-#define NS_MUST_OVERRIDE
 #endif
 
 /*
  * SEH exception macros.
  */
 #ifdef HAVE_SEH_EXCEPTIONS
 #define MOZ_SEH_TRY           __try
 #define MOZ_SEH_EXCEPT(expr)  __except(expr)