--- a/js/src/js-config.h.in
+++ b/js/src/js-config.h.in
@@ -43,28 +43,16 @@
 #undef JS_GC_ZEAL
 
 /* Define to 1 if SpiderMonkey should use small chunks. */
 #undef JS_GC_SMALL_CHUNK_SIZE
 
 /* Define to 1 to perform extra assertions and heap poisoning. */
 #undef JS_CRASH_DIAGNOSTICS
 
-/* Define to 1 if the <endian.h> header is present and
-   useable.  See jscpucfg.h.  */
-#undef JS_HAVE_ENDIAN_H
-
-/* Define to 1 if the <machine/endian.h> header is present and
-   useable.  See jscpucfg.h.  */
-#undef JS_HAVE_MACHINE_ENDIAN_H
-
-/* Define to 1 if the <sys/isa_defs.h> header is present and
-   useable.  See jscpucfg.h.  */
-#undef JS_HAVE_SYS_ISA_DEFS_H
-
 /* Define to 1 if SpiderMonkey is in NUNBOX32 mode. */
 #undef JS_NUNBOX32
 
 /* Define to 1 if SpiderMonkey is in PUNBOX64 mode. */
 #undef JS_PUNBOX64
 
 /* MOZILLA JSAPI version number components */
 #undef MOZJS_MAJOR_VERSION

--- a/js/src/jscpucfg.h
+++ b/js/src/jscpucfg.h
@@ -2,127 +2,25 @@
  * vim: set ts=8 sts=4 et sw=4 tw=99:
  * 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/. */
 
 #ifndef jscpucfg_h
 #define jscpucfg_h
 
-#define JS_HAVE_LONG_LONG
-
-#if defined(_WIN64)
+#include "mozilla/EndianUtils.h"
 
-# if defined(_M_X64) || defined(_M_AMD64) || defined(_AMD64_)
-#  define IS_LITTLE_ENDIAN 1
-#  undef  IS_BIG_ENDIAN
-# else  /* !(defined(_M_X64) || defined(_M_AMD64) || defined(_AMD64_)) */
-#  error "CPU type is unknown"
-# endif /* !(defined(_M_X64) || defined(_M_AMD64) || defined(_AMD64_)) */
-
-#elif defined(_WIN32)
-
-# ifdef __WATCOMC__
-#  define HAVE_VA_LIST_AS_ARRAY 1
-# endif
-
+#if defined(MOZ_LITTLE_ENDIAN)
 # define IS_LITTLE_ENDIAN 1
 # undef  IS_BIG_ENDIAN
-
-#elif defined(__APPLE__) || defined(__powerpc__) || defined(__ppc__)
-# if __LITTLE_ENDIAN__
-#  define IS_LITTLE_ENDIAN 1
-#  undef  IS_BIG_ENDIAN
-# elif __BIG_ENDIAN__
-#  undef  IS_LITTLE_ENDIAN
-#  define IS_BIG_ENDIAN 1
-# endif
-
-#elif defined(JS_HAVE_ENDIAN_H)
-# include <endian.h>
-
-/*
- * Historically, OSes providing <endian.h> only defined
- * __BYTE_ORDER to either __LITTLE_ENDIAN or __BIG_ENDIAN.
- * The Austin group decided to standardise <endian.h> in
- * POSIX around 2011, expecting it to provide a BYTE_ORDER
- * #define set to either LITTLE_ENDIAN or BIG_ENDIAN. We
- * should try to cope with both possibilities here.
- */
-
-# if defined(__BYTE_ORDER) || defined(BYTE_ORDER)
-#  if defined(__BYTE_ORDER)
-#   if __BYTE_ORDER == __LITTLE_ENDIAN
-#    define IS_LITTLE_ENDIAN 1
-#    undef  IS_BIG_ENDIAN
-#   elif __BYTE_ORDER == __BIG_ENDIAN
-#    undef  IS_LITTLE_ENDIAN
-#    define IS_BIG_ENDIAN 1
-#   endif
-#  endif
-#  if defined(BYTE_ORDER)
-#   if BYTE_ORDER == LITTLE_ENDIAN
-#    define IS_LITTLE_ENDIAN 1
-#    undef  IS_BIG_ENDIAN
-#   elif BYTE_ORDER == BIG_ENDIAN
-#    undef  IS_LITTLE_ENDIAN
-#    define IS_BIG_ENDIAN 1
-#   endif
-#  endif
-# else /* !defined(__BYTE_ORDER) */
-#  error "endian.h does not define __BYTE_ORDER nor BYTE_ORDER. Cannot determine endianness."
-# endif
-
-/* BSDs */
-#elif defined(JS_HAVE_MACHINE_ENDIAN_H)
-# include <sys/types.h>
-# include <machine/endian.h>
-
-# if defined(_BYTE_ORDER)
-#  if _BYTE_ORDER == _LITTLE_ENDIAN
-#   define IS_LITTLE_ENDIAN 1
-#   undef  IS_BIG_ENDIAN
-#  elif _BYTE_ORDER == _BIG_ENDIAN
-#   undef  IS_LITTLE_ENDIAN
-#   define IS_BIG_ENDIAN 1
-#  endif
-# else /* !defined(_BYTE_ORDER) */
-#  error "machine/endian.h does not define _BYTE_ORDER. Cannot determine endianness."
-# endif
-
-#elif defined(JS_HAVE_SYS_ISA_DEFS_H)
-# include <sys/isa_defs.h>
-
-# if defined(_BIG_ENDIAN)
-#  undef IS_LITTLE_ENDIAN
-#  define IS_BIG_ENDIAN 1
-# elif defined(_LITTLE_ENDIAN)
-#  define IS_LITTLE_ENDIAN 1
-#  undef IS_BIG_ENDIAN
-# else /* !defined(_LITTLE_ENDIAN) */
-#  error "sys/isa_defs.h does not define _BIG_ENDIAN or _LITTLE_ENDIAN. Cannot determine endianness."
-# endif
-# if !defined(JS_STACK_GROWTH_DIRECTION)
-#  if defined(_STACK_GROWS_UPWARD)
-#   define JS_STACK_GROWTH_DIRECTION (1)
-#  elif defined(_STACK_GROWS_DOWNWARD)
-#   define JS_STACK_GROWTH_DIRECTION (-1)
-#  endif
-# endif
-
-#elif defined(__sparc) || defined(__sparc__) || \
-      defined(_POWER) || defined(__hppa) || \
-      defined(_MIPSEB) || defined(_BIG_ENDIAN)
-/* IA64 running HP-UX will have _BIG_ENDIAN defined.
- * IA64 running Linux will have endian.h and be handled above.
- */
-# undef IS_LITTLE_ENDIAN
+#elif defined(MOZ_BIG_ENDIAN)
+# undef  IS_LITTLE_ENDIAN
 # define IS_BIG_ENDIAN 1
-
-#else /* !defined(__sparc) && !defined(__sparc__) && ... */
+#else
 # error "Cannot determine endianness of your platform. Please add support to jscpucfg.h."
 #endif
 
 #ifndef JS_STACK_GROWTH_DIRECTION
 # ifdef __hppa
 #  define JS_STACK_GROWTH_DIRECTION (1)
 # else
 #  define JS_STACK_GROWTH_DIRECTION (-1)

--- a/js/src/old-configure.in
+++ b/js/src/old-configure.in
@@ -994,31 +994,16 @@ AC_CACHE_VAL(ac_cv_type_ssize_t,
                  [ac_cv_type_ssize_t=false])])
 if test "$ac_cv_type_ssize_t" = true ; then
   AC_DEFINE(HAVE_SSIZE_T)
   AC_MSG_RESULT(yes)
 else
   AC_MSG_RESULT(no)
 fi
 
-MOZ_CHECK_HEADERS(endian.h)
-if test "$ac_cv_header_endian_h" = yes; then
-    AC_DEFINE(JS_HAVE_ENDIAN_H)
-fi
-
-MOZ_CHECK_HEADERS([machine/endian.h],[],[],[#include <sys/types.h>])
-if test "$ac_cv_header_machine_endian_h" = yes; then
-    AC_DEFINE(JS_HAVE_MACHINE_ENDIAN_H)
-fi
-
-MOZ_CHECK_HEADERS(sys/isa_defs.h)
-if test "$ac_cv_header_sys_isa_defs_h" = yes; then
-    AC_DEFINE(JS_HAVE_SYS_ISA_DEFS_H)
-fi
-
 AC_LANG_CPLUSPLUS
 
 MOZ_CXX11
 
 dnl Check for .hidden assembler directive and visibility attribute.
 dnl Borrowed from glibc configure.in
 dnl ===============================================================
 if test "$GNU_CC" -a "$OS_TARGET" != WINNT; then