--- a/widget/gtk/moz.build
+++ b/widget/gtk/moz.build
@@ -14,17 +14,17 @@ EXPORTS += [
 ]
 
 EXPORTS.mozilla += [
     'WidgetUtilsGtk.h'
 ]
 
 UNIFIED_SOURCES += [
     'IMContextWrapper.cpp',
-    'mozcontainer.c',
+    'mozcontainer.cpp',
     'NativeKeyBindings.cpp',
     'nsAppShell.cpp',
     'nsBidiKeyboard.cpp',
     'nsColorPicker.cpp',
     'nsFilePicker.cpp',
     'nsGtkKeyUtils.cpp',
     'nsImageToPixbuf.cpp',
     'nsLookAndFeel.cpp',

rename from widget/gtk/mozcontainer.c
rename to widget/gtk/mozcontainer.cpp
--- a/widget/gtk/mozcontainer.c
+++ b/widget/gtk/mozcontainer.cpp
@@ -66,17 +66,18 @@ moz_container_get_type(void)
             sizeof(MozContainer), /* instance_size */
             0, /* n_preallocs */
             (GInstanceInitFunc) moz_container_init, /* instance_init */
             NULL, /* value_table */
         };
 
         moz_container_type = g_type_register_static (GTK_TYPE_CONTAINER,
                                                      "MozContainer",
-                                                     &moz_container_info, 0);
+                                                     &moz_container_info,
+                                                     static_cast<GTypeFlags>(0));
 #ifdef ACCESSIBILITY
         /* Set a factory to return accessible object with ROLE_REDUNDANT for
          * MozContainer, so that gail won't send focus notification for it */
         atk_registry_set_factory_type(atk_get_default_registry(),
                                       moz_container_type,
                                       mai_redundant_object_factory_get_type());
 #endif
     }
@@ -84,17 +85,17 @@ moz_container_get_type(void)
     return moz_container_type;
 }
 
 GtkWidget *
 moz_container_new (void)
 {
     MozContainer *container;
 
-    container = g_object_new (MOZ_CONTAINER_TYPE, NULL);
+    container = static_cast<MozContainer*>(g_object_new (MOZ_CONTAINER_TYPE, nullptr));
 
     return GTK_WIDGET(container);
 }
 
 void
 moz_container_put (MozContainer *container, GtkWidget *child_widget,
                    gint x, gint y)
 {
@@ -285,17 +286,17 @@ moz_container_size_allocate (GtkWidget  
         return;
     }
 
     gtk_widget_set_allocation(widget, allocation);
 
     tmp_list = container->children;
 
     while (tmp_list) {
-        MozContainerChild *child = tmp_list->data;
+        MozContainerChild *child = static_cast<MozContainerChild*>(tmp_list->data);
 
         moz_container_allocate_child (container, child);
 
         tmp_list = tmp_list->next;
     }
 
     if (gtk_widget_get_has_window (widget) &&
         gtk_widget_get_realized (widget)) {
@@ -367,17 +368,17 @@ moz_container_forall (GtkContainer *cont
     g_return_if_fail (IS_MOZ_CONTAINER(container));
     g_return_if_fail (callback != NULL);
 
     moz_container = MOZ_CONTAINER(container);
 
     tmp_list = moz_container->children;
     while (tmp_list) {
         MozContainerChild *child;
-        child = tmp_list->data;
+        child = static_cast<MozContainerChild*>(tmp_list->data);
         tmp_list = tmp_list->next;
         (* callback) (child->widget, callback_data);
     }
 }
 
 static void
 moz_container_allocate_child (MozContainer *container,
                               MozContainerChild *child)
@@ -395,24 +396,23 @@ MozContainerChild *
 moz_container_get_child (MozContainer *container, GtkWidget *child_widget)
 {
     GList *tmp_list;
 
     tmp_list = container->children;
     while (tmp_list) {
         MozContainerChild *child;
     
-        child = tmp_list->data;
+        child = static_cast<MozContainerChild*>(tmp_list->data);
         tmp_list = tmp_list->next;
 
         if (child->widget == child_widget)
             return child;
     }
 
     return NULL;
 }
 
 static void 
 moz_container_add(GtkContainer *container, GtkWidget *widget)
 {
     moz_container_put(MOZ_CONTAINER(container), widget, 0, 0);
 }
-

--- a/widget/gtk/mozcontainer.h
+++ b/widget/gtk/mozcontainer.h
@@ -5,20 +5,16 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #ifndef __MOZ_CONTAINER_H__
 #define __MOZ_CONTAINER_H__
 
 #include <gtk/gtk.h>
 
-#ifdef __cplusplus
-extern "C" {
-#endif /* __cplusplus */
-
 /*
  * MozContainer
  *
  * This class serves two purposes in the nsIWidget implementation.
  *
  *   - It provides objects to receive signals from GTK for events on native
  *     windows.
  *
@@ -74,13 +70,9 @@ void       moz_container_put      (MozCo
                                    gint          y);
 void       moz_container_move          (MozContainer *container,
                                         GtkWidget    *child_widget,
                                         gint          x,
                                         gint          y,
                                         gint          width,
                                         gint          height);
 
-#ifdef __cplusplus
-}
-#endif /* __cplusplus */
-
 #endif /* __MOZ_CONTAINER_H__ */