diff --git a/xpcom/components/nsCategoryManager.h b/xpcom/components/nsCategoryManager.h
index 0bc2ee23de5..3ac7dde06fa 100644
--- a/xpcom/components/nsCategoryManager.h
+++ b/xpcom/components/nsCategoryManager.h
@@ -12,6 +12,7 @@
 #include "nsClassHashtable.h"
 #include "nsICategoryManager.h"
 #include "mozilla/Mutex.h"
+#include "mozilla/Attributes.h"
 
 #define NS_CATEGORYMANAGER_CLASSNAME     "Category Manager"
 
@@ -92,7 +93,7 @@ private:
  *
  * This implementation is thread-safe.
  */
-class nsCategoryManager
+class nsCategoryManager MOZ_FINAL
   : public nsICategoryManager
 {
 public:
diff --git a/xpcom/glue/nsThreadUtils.cpp b/xpcom/glue/nsThreadUtils.cpp
index 65356957494..97fecb01360 100644
--- a/xpcom/glue/nsThreadUtils.cpp
+++ b/xpcom/glue/nsThreadUtils.cpp
@@ -5,6 +5,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "nsThreadUtils.h"
+#include "mozilla/Attributes.h"
 
 #ifdef MOZILLA_INTERNAL_API
 # include "nsThreadManager.h"
@@ -220,7 +221,7 @@ NS_ProcessNextEvent(nsIThread *thread, bool mayWait)
 
 namespace {
 
-class nsNameThreadRunnable : public nsIRunnable
+class nsNameThreadRunnable MOZ_FINAL : public nsIRunnable
 {
 public:
   nsNameThreadRunnable(const nsACString &name) : mName(name) { }
diff --git a/xpcom/threads/LazyIdleThread.h b/xpcom/threads/LazyIdleThread.h
index 63c6faffd3f..92ed0afd0e0 100644
--- a/xpcom/threads/LazyIdleThread.h
+++ b/xpcom/threads/LazyIdleThread.h
@@ -19,6 +19,7 @@
 #include "nsCOMPtr.h"
 #include "nsTArray.h"
 #include "nsString.h"
+#include "mozilla/Attributes.h"
 
 #define IDLE_THREAD_TOPIC "thread-shutting-down"
 
@@ -31,10 +32,10 @@ namespace mozilla {
  * is created on the main thread then it will automatically join its thread on
  * XPCOM shutdown using the Observer Service.
  */
-class LazyIdleThread : public nsIThread,
-                       public nsITimerCallback,
-                       public nsIThreadObserver,
-                       public nsIObserver
+class LazyIdleThread MOZ_FINAL : public nsIThread,
+                                 public nsITimerCallback,
+                                 public nsIThreadObserver,
+                                 public nsIObserver
 {
 public:
   NS_DECL_ISUPPORTS