--- a/widget/gtk/WidgetStyleCache.cpp
+++ b/widget/gtk/WidgetStyleCache.cpp
@@ -524,16 +524,78 @@ static GtkWidget*
 CreateNotebookWidget()
 {
   GtkWidget* widget = gtk_notebook_new();
   AddToWindowContainer(widget);
   return widget;
 }
 
 static GtkWidget*
+CreateHeaderBar(WidgetNodeType aWidgetType)
+{
+  MOZ_ASSERT(gtk_check_version(3, 10, 0) == nullptr,
+             "GtkHeaderBar is only available on GTK 3.10+.");
+
+  static auto sGtkHeaderBarNewPtr = (GtkWidget* (*)())
+    dlsym(RTLD_DEFAULT, "gtk_header_bar_new");
+
+  GtkWidget* headerbar = sGtkHeaderBarNewPtr();
+  if (aWidgetType == MOZ_GTK_HEADER_BAR_MAXIMIZED) {
+    GtkWidget *window = gtk_window_new(GTK_WINDOW_POPUP);
+    gtk_widget_set_name(window, "MozillaMaximizedGtkWidget");
+    GtkStyleContext* style = gtk_widget_get_style_context(window);
+    gtk_style_context_add_class(style, "maximized");
+    GtkWidget *fixed = gtk_fixed_new();
+    gtk_container_add(GTK_CONTAINER(window), fixed);
+    gtk_container_add(GTK_CONTAINER(fixed), headerbar);
+    // Save the window container so we don't leak it.
+    sWidgetStorage[MOZ_GTK_WINDOW_MAXIMIZED] = window;
+  } else {
+    AddToWindowContainer(headerbar);
+  }
+
+  // Emulate what create_titlebar() at gtkwindow.c does.
+  GtkStyleContext* style = gtk_widget_get_style_context(headerbar);
+  gtk_style_context_add_class(style, "titlebar");
+  gtk_style_context_add_class(style, "default-decoration");
+
+  return headerbar;
+}
+
+// TODO - Also return style for buttons located at Maximized toolbar.
+static GtkWidget*
+CreateHeaderBarButton(WidgetNodeType aWidgetType)
+{
+  MOZ_ASSERT(gtk_check_version(3, 10, 0) == nullptr,
+             "GtkHeaderBar is only available on GTK 3.10+.");
+
+  GtkWidget* widget = gtk_button_new();
+  gtk_container_add(GTK_CONTAINER(GetWidget(MOZ_GTK_HEADER_BAR)), widget);
+
+  GtkStyleContext* style = gtk_widget_get_style_context(widget);
+  gtk_style_context_add_class(style, "titlebutton");
+
+  switch (aWidgetType) {
+    case MOZ_GTK_HEADER_BAR_BUTTON_CLOSE:
+      gtk_style_context_add_class(style, "close");
+      break;
+    case MOZ_GTK_HEADER_BAR_BUTTON_MINIMIZE:
+      gtk_style_context_add_class(style, "minimize");
+      break;
+    case MOZ_GTK_HEADER_BAR_BUTTON_MAXIMIZE:
+      gtk_style_context_add_class(style, "maximize");
+      break;
+    default:
+      break;
+  }
+
+  return widget;
+}
+
+static GtkWidget*
 CreateWidget(WidgetNodeType aWidgetType)
 {
   switch (aWidgetType) {
     case MOZ_GTK_WINDOW:
       return CreateWindowWidget();
     case MOZ_GTK_WINDOW_CONTAINER:
       return CreateWindowContainerWidget();
     case MOZ_GTK_CHECKBUTTON_CONTAINER:
@@ -1209,16 +1271,18 @@ ResetWidgetCache(void)
     if (sStyleStorage[i])
       g_object_unref(sStyleStorage[i]);
   }
   mozilla::PodArrayZero(sStyleStorage);
 
   /* This will destroy all of our widgets */
   if (sWidgetStorage[MOZ_GTK_WINDOW])
     gtk_widget_destroy(sWidgetStorage[MOZ_GTK_WINDOW]);
+  if (sWidgetStorage[MOZ_GTK_WINDOW_MAXIMIZED])
+    gtk_widget_destroy(sWidgetStorage[MOZ_GTK_WINDOW_MAXIMIZED]);
 
   /* Clear already freed arrays */
   mozilla::PodArrayZero(sWidgetStorage);
 }
 
 GtkStyleContext*
 GetStyleContext(WidgetNodeType aNodeType, GtkTextDirection aDirection,
                 GtkStateFlags aStateFlags, StyleFlags aFlags)