diff --git a/extensions/gio/nsGIOProtocolHandler.cpp b/extensions/gio/nsGIOProtocolHandler.cpp
index 93a2fcd7c184..5a94746b7c5a 100644
--- a/extensions/gio/nsGIOProtocolHandler.cpp
+++ b/extensions/gio/nsGIOProtocolHandler.cpp
@@ -135,7 +135,7 @@ static void mount_operation_ask_password (GMountOperation   *mount_op,
                                           gpointer          user_data);
 //-----------------------------------------------------------------------------
 
-class nsGIOInputStream : public nsIInputStream
+class nsGIOInputStream MOZ_FINAL : public nsIInputStream
 {
   public:
     NS_DECL_ISUPPORTS
@@ -880,8 +880,8 @@ mount_operation_ask_password (GMountOperation   *mount_op,
 
 //-----------------------------------------------------------------------------
 
-class nsGIOProtocolHandler : public nsIProtocolHandler
-                           , public nsIObserver
+class nsGIOProtocolHandler MOZ_FINAL : public nsIProtocolHandler
+                                     , public nsIObserver
 {
   public:
     NS_DECL_ISUPPORTS
@@ -891,7 +891,7 @@ class nsGIOProtocolHandler : public nsIProtocolHandler
     nsresult Init();
 
   private:
-    void   InitSupportedProtocolsPref(nsIPrefBranch *prefs);
+    void InitSupportedProtocolsPref(nsIPrefBranch *prefs);
     bool IsSupportedProtocol(const nsCString &spec);
 
     nsCString mSupportedProtocols;
diff --git a/toolkit/system/gnome/nsGSettingsService.cpp b/toolkit/system/gnome/nsGSettingsService.cpp
index b69b2f16de2d..c40dc490a4bd 100644
--- a/toolkit/system/gnome/nsGSettingsService.cpp
+++ b/toolkit/system/gnome/nsGSettingsService.cpp
@@ -77,7 +77,7 @@ GSETTINGS_FUNCTIONS
 
 static PRLibrary *gioLib = nullptr;
 
-class nsGSettingsCollection : public nsIGSettingsCollection
+class nsGSettingsCollection MOZ_FINAL : public nsIGSettingsCollection
 {
 public:
   NS_DECL_ISUPPORTS
diff --git a/toolkit/system/gnome/nsGSettingsService.h b/toolkit/system/gnome/nsGSettingsService.h
index 412806d2a63b..b3429bb1af25 100644
--- a/toolkit/system/gnome/nsGSettingsService.h
+++ b/toolkit/system/gnome/nsGSettingsService.h
@@ -11,7 +11,7 @@
 #define NS_GSETTINGSSERVICE_CID \
 {0xbfd4a9d8, 0xd886, 0x4161, {0x81, 0xef, 0x88, 0x68, 0xda, 0x11, 0x41, 0x70}}
 
-class nsGSettingsService : public nsIGSettingsService
+class nsGSettingsService MOZ_FINAL : public nsIGSettingsService
 {
 public:
   NS_DECL_ISUPPORTS