--- a/dom/plugins/ipc/PluginModuleChild.cpp
+++ b/dom/plugins/ipc/PluginModuleChild.cpp
@@ -19,16 +19,17 @@
 
 #include "pratom.h"
 #include "nsDebug.h"
 #include "nsCOMPtr.h"
 #include "nsPluginsDir.h"
 #include "nsXULAppAPI.h"
 
 #ifdef MOZ_X11
+# include "nsX11ErrorHandler.h"
 # include "mozilla/X11Util.h"
 #endif
 #include "mozilla/ipc/ProcessChild.h"
 #include "mozilla/plugins/PluginInstanceChild.h"
 #include "mozilla/plugins/StreamNotifyChild.h"
 #include "mozilla/plugins/BrowserStreamChild.h"
 #include "mozilla/plugins/PluginStreamChild.h"
 #include "mozilla/dom/CrashReporterChild.h"
@@ -603,17 +604,17 @@ PluginModuleChild::InitGraphics()
     real_gtk_plug_embedded = *embedded;
     *embedded = wrap_gtk_plug_embedded;
 
 #else
     // may not be necessary on all platforms
 #endif
 #ifdef MOZ_X11
     // Do this after initializing GDK, or GDK will install its own handler.
-    XRE_InstallX11ErrorHandler();
+    InstallX11ErrorHandler();
 #endif
     return true;
 }
 
 void
 PluginModuleChild::DeinitGraphics()
 {
 #if defined(MOZ_X11) && defined(NS_FREE_PERMANENT_DATA)

--- a/toolkit/xre/moz.build
+++ b/toolkit/xre/moz.build
@@ -65,16 +65,17 @@ else:
     ]
 
 if CONFIG['MOZ_WIDGET_TOOLKIT'] == 'gtk3':
     UNIFIED_SOURCES += [
         'nsGDKErrorHandler.cpp',
     ]
 
 if CONFIG['MOZ_X11']:
+    EXPORTS += ['nsX11ErrorHandler.h']
     UNIFIED_SOURCES += [
         'nsX11ErrorHandler.cpp',
     ]
 
 if CONFIG['MOZ_WIDGET_TOOLKIT'] == 'android':
     UNIFIED_SOURCES += [
         'nsAndroidStartup.cpp',
     ]

--- a/toolkit/xre/nsX11ErrorHandler.cpp
+++ b/toolkit/xre/nsX11ErrorHandler.cpp
@@ -144,21 +144,19 @@ X11Error(Display *display, XErrorEvent *
 #endif
 #endif
 
   NS_RUNTIMEABORT(notes.get());
   return 0; // not reached
 }
 }
 
-#if (MOZ_WIDGET_GTK != 3)
 void
 InstallX11ErrorHandler()
 {
   XSetErrorHandler(X11Error);
 
   Display *display = mozilla::DefaultXDisplay();
   NS_ASSERTION(display, "No X display");
   if (PR_GetEnv("MOZ_X_SYNC")) {
     XSynchronize(display, True);
   }
 }
-#endif

--- a/toolkit/xre/nsX11ErrorHandler.h
+++ b/toolkit/xre/nsX11ErrorHandler.h
@@ -1,12 +1,17 @@
 /* -*- Mode: C++; tab-width: 40; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * 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/. */
 
 #ifdef MOZ_X11
 #include <X11/Xlib.h>
-#if (MOZ_WIDGET_GTK != 3)
+
+/**
+ * InstallX11ErrorHandler is not suitable for processes running with GTK3 as
+ * GDK3 will replace the handler.  This is still used for the plugin process,
+ * which runs with GTK2.
+ **/
 void InstallX11ErrorHandler();
-#endif
+
 extern "C" int X11Error(Display *display, XErrorEvent *event);
 #endif