Index: mozilla-central/js/src/Makefile.in
===================================================================
--- mozilla-central.orig/js/src/Makefile.in
+++ js/src/Makefile.in	2011-06-20 12:19:08.010244176 +0000
@@ -462,11 +462,19 @@
     Library.cpp \
     $(NULL)
 
-LOCAL_INCLUDES = \
-    -Ictypes/libffi/include \
+ifdef MOZ_NATIVE_FFI
+LOCAL_INCLUDES = $(MOZ_FFI_CFLAGS)
+else
+LOCAL_INCLUDES = -Ictypes/libffi/include
+endif
+
+LOCAL_INCLUDES += \
     -I. \
     $(NULL)
 
+ifdef MOZ_NATIVE_FFI
+EXTRA_DSO_LDOPTS += $(MOZ_FFI_LIBS)
+else
 ifeq ($(OS_ARCH),OS2)
 SHARED_LIBRARY_LIBS += \
     ctypes/libffi/.libs/ffi.a \
@@ -476,6 +484,7 @@
     ctypes/libffi/.libs/libffi.$(LIB_SUFFIX) \
     $(NULL)
 endif
+endif
 
 endif # JS_HAS_CTYPES
 
@@ -555,6 +564,7 @@
 include $(topsrcdir)/config/rules.mk
 
 ifdef JS_HAS_CTYPES
+ifndef MOZ_NATIVE_FFI
 # Build libffi proper as part of the 'exports' target, so things get built
 # in the right order.
 export::
@@ -563,6 +573,7 @@
 distclean clean::
 		$(call SUBMAKE,$@,ctypes/libffi)
 endif
+endif
 
 # Because the SpiderMonkey can be distributed and built independently
 # of the Mozilla source tree, it contains its own copies of many of
--- mozilla-central.orig/js/src/config/autoconf.mk.in
+++ mozilla-central/js/src/config/autoconf.mk.in
@@ -250,6 +250,10 @@ NSPR_CONFIG	= @NSPR_CONFIG@
 NSPR_CFLAGS	= @NSPR_CFLAGS@
 NSPR_LIBS	= @NSPR_LIBS@
 
+MOZ_NATIVE_FFI	= @MOZ_NATIVE_FFI@
+MOZ_FFI_LIBS	= @MOZ_FFI_LIBS@
+MOZ_FFI_CFLAGS	= @MOZ_FFI_CFLAGS@
+
 USE_DEPENDENT_LIBS = @USE_DEPENDENT_LIBS@
 
 JS_NATIVE_EDITLINE = @JS_NATIVE_EDITLINE@
Index: mozilla-central/js/src/configure.in
===================================================================
--- mozilla-central.orig/js/src/configure.in
+++ mozilla-central/js/src/configure.in
@@ -4622,6 +4622,18 @@ case "${target}" in
         ;;
 esac
 
+dnl system libffi Support
+dnl ========================================================
+MOZ_ARG_ENABLE_BOOL(system-ffi,
+[  --enable-system-ffi       Use system libffi (located with pkgconfig)],
+    MOZ_NATIVE_FFI=1 )
+
+if test -n "$MOZ_NATIVE_FFI"; then
+    PKG_CHECK_MODULES(MOZ_FFI, libffi)
+fi
+
+AC_SUBST(MOZ_NATIVE_FFI)
+
 dnl ========================================================
 dnl Use ARM userspace kernel helpers; tell NSPR to enable
 dnl their usage and use them in spidermonkey.
@@ -6010,7 +6022,7 @@ AC_MSG_RESULT(invoking make to create js
 $GMAKE js-config
 
 # Build jsctypes if it's enabled.
-if test "$JS_HAS_CTYPES"; then
+if test "$JS_HAS_CTYPES" -a -z "$MOZ_NATIVE_FFI"; then
   # Run the libffi 'configure' script.
   ac_configure_args="--disable-shared --enable-static --disable-raw-api"
   if test "$MOZ_DEBUG"; then
Index: mozilla-central/js/src/shell/Makefile.in
===================================================================
--- mozilla-central.orig/js/src/shell/Makefile.in
+++ mozilla-central/js/src/shell/Makefile.in
@@ -53,6 +53,9 @@ CPPSRCS		= \
 DEFINES         += -DEXPORT_JS_API
 
 LIBS      = $(NSPR_LIBS) $(EDITLINE_LIBS) $(DEPTH)/$(LIB_PREFIX)js_static.$(LIB_SUFFIX)
+ifdef MOZ_NATIVE_FFI
+EXTRA_LIBS += $(MOZ_FFI_LIBS)
+endif
 
 LOCAL_INCLUDES += -I$(topsrcdir) -I..