diff --git a/caps/nsNullPrincipalURI.h b/caps/nsNullPrincipalURI.h
index 02ea20106cbe..72baf06d79ee 100644
--- a/caps/nsNullPrincipalURI.h
+++ b/caps/nsNullPrincipalURI.h
@@ -31,8 +31,8 @@ public:
   NS_DECL_NSIURI
 
   // nsISizeOf
-  virtual size_t SizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf) const;
-  virtual size_t SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf) const;
+  virtual size_t SizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf) const MOZ_OVERRIDE;
+  virtual size_t SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf) const MOZ_OVERRIDE;
 
   explicit nsNullPrincipalURI(const nsCString &aSpec);
 
diff --git a/caps/nsPrincipal.h b/caps/nsPrincipal.h
index 634edbb806e3..8d748ea58230 100644
--- a/caps/nsPrincipal.h
+++ b/caps/nsPrincipal.h
@@ -49,25 +49,25 @@ class nsPrincipal MOZ_FINAL : public nsBasePrincipal
 public:
   NS_DECL_ISUPPORTS_INHERITED
   NS_DECL_NSISERIALIZABLE
-  NS_IMETHOD Equals(nsIPrincipal* other, bool* _retval);
-  NS_IMETHOD EqualsConsideringDomain(nsIPrincipal* other, bool* _retval);
-  NS_IMETHOD GetHashValue(uint32_t* aHashValue);
-  NS_IMETHOD GetURI(nsIURI** aURI);
-  NS_IMETHOD GetDomain(nsIURI** aDomain);
-  NS_IMETHOD SetDomain(nsIURI* aDomain);
-  NS_IMETHOD GetOrigin(char** aOrigin);
-  NS_IMETHOD Subsumes(nsIPrincipal* other, bool* _retval);
-  NS_IMETHOD SubsumesConsideringDomain(nsIPrincipal* other, bool* _retval);
-  NS_IMETHOD CheckMayLoad(nsIURI* uri, bool report, bool allowIfInheritsPrincipal);
-  NS_IMETHOD GetJarPrefix(nsACString& aJarPrefix);
-  NS_IMETHOD GetAppStatus(uint16_t* aAppStatus);
-  NS_IMETHOD GetAppId(uint32_t* aAppStatus);
-  NS_IMETHOD GetIsInBrowserElement(bool* aIsInBrowserElement);
-  NS_IMETHOD GetUnknownAppId(bool* aUnknownAppId);
-  NS_IMETHOD GetIsNullPrincipal(bool* aIsNullPrincipal);
-  NS_IMETHOD GetBaseDomain(nsACString& aBaseDomain);
+  NS_IMETHOD Equals(nsIPrincipal* other, bool* _retval) MOZ_OVERRIDE;
+  NS_IMETHOD EqualsConsideringDomain(nsIPrincipal* other, bool* _retval) MOZ_OVERRIDE;
+  NS_IMETHOD GetHashValue(uint32_t* aHashValue) MOZ_OVERRIDE;
+  NS_IMETHOD GetURI(nsIURI** aURI) MOZ_OVERRIDE;
+  NS_IMETHOD GetDomain(nsIURI** aDomain) MOZ_OVERRIDE;
+  NS_IMETHOD SetDomain(nsIURI* aDomain) MOZ_OVERRIDE;
+  NS_IMETHOD GetOrigin(char** aOrigin) MOZ_OVERRIDE;
+  NS_IMETHOD Subsumes(nsIPrincipal* other, bool* _retval) MOZ_OVERRIDE;
+  NS_IMETHOD SubsumesConsideringDomain(nsIPrincipal* other, bool* _retval) MOZ_OVERRIDE;
+  NS_IMETHOD CheckMayLoad(nsIURI* uri, bool report, bool allowIfInheritsPrincipal) MOZ_OVERRIDE;
+  NS_IMETHOD GetJarPrefix(nsACString& aJarPrefix) MOZ_OVERRIDE;
+  NS_IMETHOD GetAppStatus(uint16_t* aAppStatus) MOZ_OVERRIDE;
+  NS_IMETHOD GetAppId(uint32_t* aAppStatus) MOZ_OVERRIDE;
+  NS_IMETHOD GetIsInBrowserElement(bool* aIsInBrowserElement) MOZ_OVERRIDE;
+  NS_IMETHOD GetUnknownAppId(bool* aUnknownAppId) MOZ_OVERRIDE;
+  NS_IMETHOD GetIsNullPrincipal(bool* aIsNullPrincipal) MOZ_OVERRIDE;
+  NS_IMETHOD GetBaseDomain(nsACString& aBaseDomain) MOZ_OVERRIDE;
 #ifdef DEBUG
-  virtual void dumpImpl();
+  virtual void dumpImpl() MOZ_OVERRIDE;
 #endif
 
   nsPrincipal();
@@ -132,25 +132,25 @@ public:
   NS_DECL_ISUPPORTS_INHERITED
   NS_DECL_NSIEXPANDEDPRINCIPAL
   NS_DECL_NSISERIALIZABLE
-  NS_IMETHOD Equals(nsIPrincipal* other, bool* _retval);
-  NS_IMETHOD EqualsConsideringDomain(nsIPrincipal* other, bool* _retval);
-  NS_IMETHOD GetHashValue(uint32_t* aHashValue);
-  NS_IMETHOD GetURI(nsIURI** aURI);
-  NS_IMETHOD GetDomain(nsIURI** aDomain);
-  NS_IMETHOD SetDomain(nsIURI* aDomain);
-  NS_IMETHOD GetOrigin(char** aOrigin);
-  NS_IMETHOD Subsumes(nsIPrincipal* other, bool* _retval);
-  NS_IMETHOD SubsumesConsideringDomain(nsIPrincipal* other, bool* _retval);
-  NS_IMETHOD CheckMayLoad(nsIURI* uri, bool report, bool allowIfInheritsPrincipal);
-  NS_IMETHOD GetJarPrefix(nsACString& aJarPrefix);
-  NS_IMETHOD GetAppStatus(uint16_t* aAppStatus);
-  NS_IMETHOD GetAppId(uint32_t* aAppStatus);
-  NS_IMETHOD GetIsInBrowserElement(bool* aIsInBrowserElement);
-  NS_IMETHOD GetUnknownAppId(bool* aUnknownAppId);
-  NS_IMETHOD GetIsNullPrincipal(bool* aIsNullPrincipal);
-  NS_IMETHOD GetBaseDomain(nsACString& aBaseDomain);
+  NS_IMETHOD Equals(nsIPrincipal* other, bool* _retval) MOZ_OVERRIDE;
+  NS_IMETHOD EqualsConsideringDomain(nsIPrincipal* other, bool* _retval) MOZ_OVERRIDE;
+  NS_IMETHOD GetHashValue(uint32_t* aHashValue) MOZ_OVERRIDE;
+  NS_IMETHOD GetURI(nsIURI** aURI) MOZ_OVERRIDE;
+  NS_IMETHOD GetDomain(nsIURI** aDomain) MOZ_OVERRIDE;
+  NS_IMETHOD SetDomain(nsIURI* aDomain) MOZ_OVERRIDE;
+  NS_IMETHOD GetOrigin(char** aOrigin) MOZ_OVERRIDE;
+  NS_IMETHOD Subsumes(nsIPrincipal* other, bool* _retval) MOZ_OVERRIDE;
+  NS_IMETHOD SubsumesConsideringDomain(nsIPrincipal* other, bool* _retval) MOZ_OVERRIDE;
+  NS_IMETHOD CheckMayLoad(nsIURI* uri, bool report, bool allowIfInheritsPrincipal) MOZ_OVERRIDE;
+  NS_IMETHOD GetJarPrefix(nsACString& aJarPrefix) MOZ_OVERRIDE;
+  NS_IMETHOD GetAppStatus(uint16_t* aAppStatus) MOZ_OVERRIDE;
+  NS_IMETHOD GetAppId(uint32_t* aAppStatus) MOZ_OVERRIDE;
+  NS_IMETHOD GetIsInBrowserElement(bool* aIsInBrowserElement) MOZ_OVERRIDE;
+  NS_IMETHOD GetUnknownAppId(bool* aUnknownAppId) MOZ_OVERRIDE;
+  NS_IMETHOD GetIsNullPrincipal(bool* aIsNullPrincipal) MOZ_OVERRIDE;
+  NS_IMETHOD GetBaseDomain(nsACString& aBaseDomain) MOZ_OVERRIDE;
 #ifdef DEBUG
-  virtual void dumpImpl();
+  virtual void dumpImpl() MOZ_OVERRIDE;
 #endif
   
   virtual void GetScriptLocation(nsACString &aStr) MOZ_OVERRIDE;
diff --git a/docshell/base/IHistory.h b/docshell/base/IHistory.h
index 781eb79eb041..4ad0693dcb2c 100644
--- a/docshell/base/IHistory.h
+++ b/docshell/base/IHistory.h
@@ -132,14 +132,14 @@ NS_DEFINE_STATIC_IID_ACCESSOR(IHistory, IHISTORY_IID)
 
 #define NS_DECL_IHISTORY \
     NS_IMETHOD RegisterVisitedCallback(nsIURI *aURI, \
-                                       mozilla::dom::Link *aContent); \
+                                       mozilla::dom::Link *aContent) MOZ_OVERRIDE; \
     NS_IMETHOD UnregisterVisitedCallback(nsIURI *aURI, \
-                                         mozilla::dom::Link *aContent); \
+                                         mozilla::dom::Link *aContent) MOZ_OVERRIDE; \
     NS_IMETHOD VisitURI(nsIURI *aURI, \
                         nsIURI *aLastVisitedURI, \
-                        uint32_t aFlags); \
-    NS_IMETHOD SetURITitle(nsIURI* aURI, const nsAString& aTitle); \
-    NS_IMETHOD NotifyVisited(nsIURI* aURI);
+                        uint32_t aFlags) MOZ_OVERRIDE; \
+    NS_IMETHOD SetURITitle(nsIURI* aURI, const nsAString& aTitle) MOZ_OVERRIDE; \
+    NS_IMETHOD NotifyVisited(nsIURI* aURI) MOZ_OVERRIDE;
 
 } // namespace mozilla
 
diff --git a/dom/audiochannel/tests/TestAudioChannelService.cpp b/dom/audiochannel/tests/TestAudioChannelService.cpp
index a9058d5d8bc0..238219847338 100644
--- a/dom/audiochannel/tests/TestAudioChannelService.cpp
+++ b/dom/audiochannel/tests/TestAudioChannelService.cpp
@@ -103,14 +103,14 @@ public:
     return mAgent->SetVisibilityState(visible);
   }
 
-  NS_IMETHODIMP CanPlayChanged(int32_t canPlay)
+  NS_IMETHODIMP CanPlayChanged(int32_t canPlay) MOZ_OVERRIDE
   {
     mCanPlay = static_cast<AudioChannelState>(canPlay);
     mWaitCallback = false;
     return NS_OK;
   }
 
-  NS_IMETHODIMP WindowVolumeChanged()
+  NS_IMETHODIMP WindowVolumeChanged() MOZ_OVERRIDE
   {
     return NS_OK;
   }
diff --git a/extensions/cookie/nsPermissionManager.cpp b/extensions/cookie/nsPermissionManager.cpp
index 9d2deab262a4..d288078e4ab0 100644
--- a/extensions/cookie/nsPermissionManager.cpp
+++ b/extensions/cookie/nsPermissionManager.cpp
@@ -193,7 +193,7 @@ public:
 
   // nsIObserver implementation.
   NS_IMETHODIMP
-  Observe(nsISupports *aSubject, const char *aTopic, const char16_t *data)
+  Observe(nsISupports *aSubject, const char *aTopic, const char16_t *data) MOZ_OVERRIDE
   {
     MOZ_ASSERT(!nsCRT::strcmp(aTopic, "webapps-clear-data"));
 
diff --git a/extensions/universalchardet/src/xpcom/nsUdetXPCOMWrapper.h b/extensions/universalchardet/src/xpcom/nsUdetXPCOMWrapper.h
index cd1306f98d0e..7e43fb046e91 100644
--- a/extensions/universalchardet/src/xpcom/nsUdetXPCOMWrapper.h
+++ b/extensions/universalchardet/src/xpcom/nsUdetXPCOMWrapper.h
@@ -29,12 +29,12 @@ class nsXPCOMDetector :
   NS_DECL_ISUPPORTS
   public:
     nsXPCOMDetector();
-    NS_IMETHOD Init(nsICharsetDetectionObserver* aObserver);
-    NS_IMETHOD DoIt(const char* aBuf, uint32_t aLen, bool *oDontFeedMe);
-    NS_IMETHOD Done();
+    NS_IMETHOD Init(nsICharsetDetectionObserver* aObserver) MOZ_OVERRIDE;
+    NS_IMETHOD DoIt(const char* aBuf, uint32_t aLen, bool *oDontFeedMe) MOZ_OVERRIDE;
+    NS_IMETHOD Done() MOZ_OVERRIDE;
   protected:
     virtual ~nsXPCOMDetector();
-    virtual void Report(const char* aCharset);
+    virtual void Report(const char* aCharset) MOZ_OVERRIDE;
   private:
     nsCOMPtr<nsICharsetDetectionObserver> mObserver;
 };
@@ -49,10 +49,10 @@ class nsXPCOMStringDetector :
   public:
     nsXPCOMStringDetector();
     NS_IMETHOD DoIt(const char* aBuf, uint32_t aLen, 
-                    const char** oCharset, nsDetectionConfident &oConf);
+                    const char** oCharset, nsDetectionConfident &oConf) MOZ_OVERRIDE;
   protected:
     virtual ~nsXPCOMStringDetector();
-    virtual void Report(const char* aCharset);
+    virtual void Report(const char* aCharset) MOZ_OVERRIDE;
   private:
     nsCOMPtr<nsICharsetDetectionObserver> mObserver;
     const char* mResult;
diff --git a/hal/sandbox/SandboxHal.cpp b/hal/sandbox/SandboxHal.cpp
index 3bb2360100aa..d19b0375d3b0 100644
--- a/hal/sandbox/SandboxHal.cpp
+++ b/hal/sandbox/SandboxHal.cpp
@@ -570,7 +570,7 @@ public:
     return true;
   }
 
-  void Notify(const NetworkInformation& aNetworkInfo) {
+  void Notify(const NetworkInformation& aNetworkInfo) MOZ_OVERRIDE {
     unused << SendNotifyNetworkChange(aNetworkInfo);
   }
 
@@ -612,7 +612,7 @@ public:
     return true;
   }
 
-  void Notify(const ScreenConfiguration& aScreenConfiguration) {
+  void Notify(const ScreenConfiguration& aScreenConfiguration) MOZ_OVERRIDE {
     unused << SendNotifyScreenConfigurationChange(aScreenConfiguration);
   }
 
@@ -778,7 +778,7 @@ public:
     return true;
   }
   
-  void Notify(const SensorData& aSensorData) {
+  void Notify(const SensorData& aSensorData) MOZ_OVERRIDE {
     unused << SendNotifySensorChange(aSensorData);
   }
 
@@ -817,7 +817,7 @@ public:
     return true;
   }
   
-  void Notify(const WakeLockInformation& aWakeLockInfo)
+  void Notify(const WakeLockInformation& aWakeLockInfo) MOZ_OVERRIDE
   {
     unused << SendNotifyWakeLockChange(aWakeLockInfo);
   }
@@ -837,7 +837,7 @@ public:
     return true;
   }
 
-  void Notify(const SwitchEvent& aSwitchEvent)
+  void Notify(const SwitchEvent& aSwitchEvent) MOZ_OVERRIDE
   {
     unused << SendNotifySwitchChange(aSwitchEvent);
   }
@@ -850,12 +850,12 @@ public:
     return true;
   }
 
-  void Notify(const int64_t& aClockDeltaMS)
+  void Notify(const int64_t& aClockDeltaMS) MOZ_OVERRIDE
   {
     unused << SendNotifySystemClockChange(aClockDeltaMS);
   }
 
-  void Notify(const SystemTimezoneChangeInformation& aSystemTimezoneChangeInfo)
+  void Notify(const SystemTimezoneChangeInformation& aSystemTimezoneChangeInfo) MOZ_OVERRIDE
   {
     unused << SendNotifySystemTimezoneChange(aSystemTimezoneChangeInfo);
   }
@@ -938,14 +938,14 @@ public:
   }
 
   virtual bool
-  RecvNotifySystemClockChange(const int64_t& aClockDeltaMS) {
+  RecvNotifySystemClockChange(const int64_t& aClockDeltaMS) MOZ_OVERRIDE {
     hal::NotifySystemClockChange(aClockDeltaMS);
     return true;
   }
 
   virtual bool
   RecvNotifySystemTimezoneChange(
-    const SystemTimezoneChangeInformation& aSystemTimezoneChangeInfo) {
+    const SystemTimezoneChangeInformation& aSystemTimezoneChangeInfo) MOZ_OVERRIDE {
     hal::NotifySystemTimezoneChange(aSystemTimezoneChangeInfo);
     return true;
   }
diff --git a/image/src/MultipartImage.cpp b/image/src/MultipartImage.cpp
index 11b234a565ab..706b24dcdc5d 100644
--- a/image/src/MultipartImage.cpp
+++ b/image/src/MultipartImage.cpp
@@ -18,7 +18,7 @@ class NextPartObserver : public IProgressObserver
 {
 public:
   MOZ_DECLARE_REFCOUNTED_TYPENAME(NextPartObserver)
-  NS_INLINE_DECL_REFCOUNTING(NextPartObserver)
+  NS_INLINE_DECL_REFCOUNTING(NextPartObserver, MOZ_OVERRIDE)
 
   explicit NextPartObserver(MultipartImage* aOwner)
     : mOwner(aOwner)
diff --git a/storage/test/test_async_callbacks_with_spun_event_loops.cpp b/storage/test/test_async_callbacks_with_spun_event_loops.cpp
index 063997ae5477..9fe7d9953c3d 100644
--- a/storage/test/test_async_callbacks_with_spun_event_loops.cpp
+++ b/storage/test/test_async_callbacks_with_spun_event_loops.cpp
@@ -58,7 +58,7 @@ private:
   }
 
 public:
-  NS_IMETHOD HandleResult(mozIStorageResultSet* aResultSet)
+  NS_IMETHOD HandleResult(mozIStorageResultSet* aResultSet) MOZ_OVERRIDE
   {
     sResult = true;
     spin_events_loop_until_true(&mCompleted);
@@ -68,7 +68,7 @@ public:
     return NS_OK;
   }
 
-  NS_IMETHOD HandleError(mozIStorageError* aError)
+  NS_IMETHOD HandleError(mozIStorageError* aError) MOZ_OVERRIDE
   {
     sError = true;
     spin_events_loop_until_true(&mCompleted);
@@ -78,7 +78,7 @@ public:
     return NS_OK;
   }
 
-  NS_IMETHOD HandleCompletion(uint16_t aReason)
+  NS_IMETHOD HandleCompletion(uint16_t aReason) MOZ_OVERRIDE
   {
     mCompleted = true;
     return NS_OK;