diff --git a/dom/plugins/base/nsPluginNativeWindowGtk.cpp b/dom/plugins/base/nsPluginNativeWindowGtk.cpp

--- a/dom/plugins/base/nsPluginNativeWindowGtk.cpp

+++ b/dom/plugins/base/nsPluginNativeWindowGtk.cpp

@@ -19,16 +19,17 @@

 #if (GTK_MAJOR_VERSION == 3)

 #include <gtk/gtkx.h>

 #else

 #include "gtk2xtbin.h"

 #endif

 #include "mozilla/X11Util.h"

+static void plug_added_cb(GtkWidget *widget, gpointer data);

 static gboolean plug_removed_cb   (GtkWidget *widget, gpointer data);

 static void socket_unrealize_cb   (GtkWidget *widget, gpointer data);

 nsPluginNativeWindowGtk::nsPluginNativeWindowGtk() : nsPluginNativeWindow()

 {

   // initialize the struct fields

   window = nullptr; 

   x = 0; 

@@ -158,16 +159,19 @@ nsresult nsPluginNativeWindowGtk::Create

   //attach the socket to the container widget

   gtk_widget_set_parent_window(mSocketWidget, parent_win);

   // enable/disable focus event handlers,

   // see plugin_window_filter_func() for details

   g_object_set_data(G_OBJECT(mSocketWidget), "enable-xt-focus", (void *)aEnableXtFocus);

+  g_signal_connect(mSocketWidget, "plug_added",

+                   G_CALLBACK(plug_added_cb), nullptr);

+

   // Make sure to handle the plug_removed signal.  If we don't the

   // socket will automatically be destroyed when the plug is

   // removed, which means we're destroying it more than once.

   // SYNTAX ERROR.

   g_signal_connect(mSocketWidget, "plug_removed",

                    G_CALLBACK(plug_removed_cb), nullptr);

   g_signal_connect(mSocketWidget, "unrealize",

@@ -273,16 +277,42 @@ nsresult nsPluginNativeWindowGtk::Create

   // Leave mWsInfo.type = 0 - Who knows what this is meant to be?

   XFlush(mWsInfo.display);

   return NS_OK;

 }

 #endif

+static void

+plug_window_finalize_cb(gpointer socket, GObject* plug_window)

+{

+  g_object_unref(socket);

+}

+

+static void

+plug_added_cb(GtkWidget *socket, gpointer data)

+{

+  // The plug window has been embedded, and gtk_socket_add_window() has added

+  // a filter to the socket's plug_window, passing the socket as data for the

+  // filter, so the socket must live as long as events may be received on the

+  // plug window.

+  //

+  // https://git.gnome.org/browse/gtk+/tree/gtk/gtksocket.c?h=3.18.7#n1124

+  g_object_ref(socket);

+  // When the socket is unrealized, perhaps during gtk_widget_destroy() from

+  // ~nsPluginNativeWindowGtk, the plug is removed.  The plug in the child

+  // process then destroys its widget and window.  When the browser process

+  // receives the DestroyNotify event for the plug window, GDK releases its

+  // reference to plugWindow.  This is typically the last reference and so the

+  // weak ref callback triggers release of the socket.

+  GdkWindow* plugWindow = gtk_socket_get_plug_window(GTK_SOCKET(socket));

+  g_object_weak_ref(G_OBJECT(plugWindow), plug_window_finalize_cb, socket);

+}

+

 /* static */

 gboolean

 plug_removed_cb (GtkWidget *widget, gpointer data)

 {

   // Gee, thanks for the info!

   return TRUE;

 }

diff --git a/widget/gtk/mozgtk/mozgtk.c b/widget/gtk/mozgtk/mozgtk.c

--- a/widget/gtk/mozgtk/mozgtk.c

+++ b/widget/gtk/mozgtk/mozgtk.c

@@ -384,16 +384,17 @@ STUB(gtk_selection_data_targets_include_

 STUB(gtk_separator_get_type)

 STUB(gtk_separator_menu_item_new)

 STUB(gtk_separator_tool_item_new)

 STUB(gtk_settings_get_default)

 STUB(gtk_settings_get_for_screen)

 STUB(gtk_socket_add_id)

 STUB(gtk_socket_get_id)

 STUB(gtk_socket_get_type)

+STUB(gtk_socket_get_plug_window)

 STUB(gtk_socket_new)

 STUB(gtk_spin_button_new)

 STUB(gtk_statusbar_new)

 STUB(gtk_style_lookup_icon_set)

 STUB(gtk_table_attach)

 STUB(gtk_table_get_type)

 STUB(gtk_table_new)

 STUB(gtk_target_list_add)