diff --git a/config/recurse.mk b/config/recurse.mk
index c7bb531c6e..fad227aead 100644
--- a/config/recurse.mk
+++ b/config/recurse.mk
@@ -155,8 +155,10 @@ endif
 # Interdependencies that moz.build world don't know about yet for compilation.
 # Note some others are hardcoded or "guessed" in recursivemake.py and emitter.py
 ifeq ($(MOZ_WIDGET_TOOLKIT),gtk3)
+ifdef MOZ_ENABLE_NPAPI
 toolkit/library/target: widget/gtk/mozgtk/gtk3/target
 endif
+endif
 ifdef MOZ_LDAP_XPCOM
 ldap/target: security/target mozglue/build/target
 toolkit/library/target: ldap/target
diff --git a/mozglue/build/gtk.c b/mozglue/build/gtk.c
new file mode 100644
index 0000000000..b5b1b4be88
--- /dev/null
+++ b/mozglue/build/gtk.c
@@ -0,0 +1,19 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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/. */
+
+#include "mozilla/Types.h"
+
+// Only define the following workaround when using GTK3, which we detect
+// by checking if GTK3 stubs are not provided.
+#include <X11/Xlib.h>
+// Bug 1271100
+// We need to trick system Cairo into not using the XShm extension due to
+// a race condition in it that results in frequent BadAccess errors. Cairo
+// relies upon XShmQueryExtension to initially detect if XShm is available.
+// So we define our own stub that always indicates XShm not being present.
+// mozgtk loads before libXext/libcairo and so this stub will take priority.
+// Our tree usage goes through xcb and remains unaffected by this.
+MFBT_API Bool XShmQueryExtension(Display* aDisplay) { return False; }
diff --git a/mozglue/build/moz.build b/mozglue/build/moz.build
index 9197eda1bc..e291e472ae 100644
--- a/mozglue/build/moz.build
+++ b/mozglue/build/moz.build
@@ -15,6 +15,9 @@ SDK_LIBRARY = True
 if CONFIG['MOZ_ASAN']:
     SOURCES += ['AsanOptions.cpp']
 
+if not CONFIG['MOZ_ENABLE_NPAPI'] and CONFIG['MOZ_WIDGET_TOOLKIT'] == 'gtk3':
+    SOURCES += ['gtk.c']
+
 if CONFIG['OS_TARGET'] == 'WINNT':
     DEFFILE = 'mozglue.def'
     # We'll break the DLL blocklist if we immediately load user32.dll
diff --git a/old-configure.in b/old-configure.in
index b5e4428dbd..ce3dd1b7f5 100644
--- a/old-configure.in
+++ b/old-configure.in
@@ -2122,6 +2122,24 @@ if test -z "$XULRUNNER_STUB_NAME"; then
 fi
 AC_SUBST(XULRUNNER_STUB_NAME)
 
+dnl ========================================================
+dnl = NPAPI support
+dnl ========================================================
+
+MOZ_ENABLE_NPAPI=1
+
+MOZ_ARG_DISABLE_BOOL(npapi,
+[  --disable-npapi          Disable NPAPI support ],
+    MOZ_ENABLE_NPAPI=,
+    MOZ_ENABLE_NPAPI=1)
+
+if test "$MOZ_ENABLE_NPAPI"
+then
+    AC_DEFINE(MOZ_ENABLE_NPAPI)
+fi
+
+AC_SUBST(MOZ_ENABLE_NPAPI)
+
 dnl ========================================================
 dnl =
 dnl = Toolkit Options
@@ -2189,9 +2207,15 @@ if test "$COMPILE_ENVIRONMENT"; then
     dnl are suppressed by widget/gtk/compat-gtk3/gdk/gdkversionmacros.h.
     AC_DEFINE_UNQUOTED(GDK_VERSION_MAX_ALLOWED,$GDK_VERSION_MAX_ALLOWED)
     GLIB_VERSION_MAX_ALLOWED=GLIB_VERSION_2_32
+    dnl We want to check GTK2 packages if NPAPI is enabled, even if building with GTK3.
+    if test "$MOZ_ENABLE_NPAPI"; then
+      MOZ_CHECK_GTK2=1
+    fi
   fi
   if test "$MOZ_WIDGET_TOOLKIT" = gtk2; then
     GLIB_VERSION_MAX_ALLOWED=$GLIB_VERSION_MIN_REQUIRED
+    dnl Check GTK2 packages if we're building against GTK2, whether NPAPI is disabled or not.
+    MOZ_CHECK_GTK2=1
   fi
   if test "$MOZ_ENABLE_GTK"; then
     if test "$MOZ_X11"; then
@@ -2200,8 +2224,11 @@ if test "$COMPILE_ENVIRONMENT"; then
     AC_DEFINE_UNQUOTED(GLIB_VERSION_MIN_REQUIRED,$GLIB_VERSION_MIN_REQUIRED)
     AC_DEFINE_UNQUOTED(GLIB_VERSION_MAX_ALLOWED,$GLIB_VERSION_MAX_ALLOWED)
 
-    PKG_CHECK_MODULES(MOZ_GTK2, gtk+-2.0 >= $GTK2_VERSION gtk+-unix-print-2.0 glib-2.0 >= $GLIB_VERSION gobject-2.0 $GDK_PACKAGES)
+    if test "$MOZ_CHECK_GTK2"; then
+      PKG_CHECK_MODULES(MOZ_GTK2, gtk+-2.0 >= $GTK2_VERSION gtk+-unix-print-2.0 glib-2.0 >= $GLIB_VERSION gobject-2.0 $GDK_PACKAGES, ,
+                               [AC_MSG_ERROR([ * * * Could not find gtk+-2.0. Required for NPAPI plugins. To build without NPAPI, add --disable-npapi to your .mozconfig and clobber.])])
     MOZ_GTK2_CFLAGS="-I${_topsrcdir}/widget/gtk/compat $MOZ_GTK2_CFLAGS"
+    fi
   fi
   if test "$MOZ_WIDGET_TOOLKIT" = gtk2; then
     TK_CFLAGS=$MOZ_GTK2_CFLAGS
@@ -2491,24 +2518,6 @@ then
 fi
 AC_SUBST(MOZ_ENABLE_DBUS)
 
-dnl ========================================================
-dnl = NPAPI support
-dnl ========================================================
-
-MOZ_ENABLE_NPAPI=1
-
-MOZ_ARG_DISABLE_BOOL(npapi,
-[  --disable-npapi          Disable NPAPI support ],
-    MOZ_ENABLE_NPAPI=,
-    MOZ_ENABLE_NPAPI=1)
-
-if test "$MOZ_ENABLE_NPAPI"
-then
-    AC_DEFINE(MOZ_ENABLE_NPAPI)
-fi
-
-AC_SUBST(MOZ_ENABLE_NPAPI)
-
 dnl =========================================================
 dnl = Whether to exclude hyphenations files in the build
 dnl =========================================================
diff --git a/toolkit/library/moz.build b/toolkit/library/moz.build
index 504600cfbc..06cc3598e2 100644
--- a/toolkit/library/moz.build
+++ b/toolkit/library/moz.build
@@ -116,11 +116,14 @@ if CONFIG['USE_ICU']:
         'icu',
     ]
 
-if CONFIG['MOZ_WIDGET_TOOLKIT'] == 'gtk3':
+if CONFIG['MOZ_WIDGET_TOOLKIT'] == 'gtk3' and CONFIG['MOZ_ENABLE_NPAPI']:
     USE_LIBS += [
         'mozgtk_stub',
     ]
 
+if CONFIG['MOZ_WIDGET_TOOLKIT'] == 'gtk3' and not CONFIG['MOZ_ENABLE_NPAPI']:
+    OS_LIBS += CONFIG['MOZ_GTK3_LIBS']
+
 if CONFIG['MOZ_WIDGET_TOOLKIT'] == 'cocoa':
     CXXFLAGS += CONFIG['TK_CFLAGS']
 
diff --git a/widget/gtk/moz.build b/widget/gtk/moz.build
index 7c802a3c1e..a948b46445 100644
--- a/widget/gtk/moz.build
+++ b/widget/gtk/moz.build
@@ -3,7 +3,7 @@
 # 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/.
 
-if CONFIG['MOZ_WIDGET_TOOLKIT'] == 'gtk3':
+if CONFIG['MOZ_WIDGET_TOOLKIT'] == 'gtk3' and CONFIG['MOZ_ENABLE_NPAPI']:
     DIRS += ['mozgtk']
 
 EXPORTS += [
diff --git a/widget/moz.build b/widget/moz.build
index 2ba398c260..e81c175254 100644
--- a/widget/moz.build
+++ b/widget/moz.build
@@ -52,7 +52,7 @@ if toolkit in ('cocoa', 'gtk2', 'gtk3'):
 if 'gtk' in CONFIG['MOZ_WIDGET_TOOLKIT']:
     DIRS += ['gtk']
 
-    if CONFIG['MOZ_X11']:
+    if CONFIG['MOZ_X11'] and CONFIG['MOZ_ENABLE_NPAPI']:
         DIRS += ['gtkxtbin']
 
 XPIDL_SOURCES += [