--- a/configure.in
+++ b/configure.in
@@ -8279,21 +8279,24 @@ echo $MAKEFILES | ${PERL} $srcdir/build/
 else
 echo $MAKEFILES | ${PERL} $srcdir/build/autoconf/acoutput-fast.pl -nowrap --cygwin-srcdir=$srcdir > conftest.sh
 fi
 . ./conftest.sh
 rm conftest.sh
 
 echo $MAKEFILES > unallmakefiles
 
+mv -f config/autoconf.mk config/autoconf.mk.orig 2> /dev/null
+
 AC_OUTPUT($MAKEFILES)
 
 dnl Prevent the regeneration of cairo-features.h forcing rebuilds of gfx stuff
 if test "$CAIRO_FEATURES_H"; then
   if cmp -s $CAIRO_FEATURES_H "$CAIRO_FEATURES_H".orig; then
+    echo "$CAIRO_FEATURES_H is unchanged"
     mv -f "$CAIRO_FEATURES_H".orig "$CAIRO_FEATURES_H" 2> /dev/null
   else
     rm -f "$CAIRO_FEATURES_H".orig 2> /dev/null
   fi
 fi
 
 dnl ========================================================
 dnl = Setup a nice relatively clean build environment for
@@ -8364,8 +8367,17 @@ ac_configure_args="$ac_configure_args --
 ac_configure_args="$ac_configure_args --with-sync-build-files=$_topsrcdir"
 if test "$MOZ_MEMORY"; then
    ac_configure_args="$ac_configure_args --enable-jemalloc"  
 fi
 AC_OUTPUT_SUBDIRS(js/src)
 ac_configure_args="$_SUBDIR_CONFIG_ARGS"
 
 fi # COMPILE_ENVIRONMENT && !LIBXUL_SDK_DIR
+
+dnl Prevent the regeneration of autoconf.mk forcing rebuilds of the world
+dnl Needs to be at the end to respect possible changes from NSPR configure
+if cmp -b config/autoconf.mk config/autoconf.mk.orig; then
+  echo "config/autoconf.mk is unchanged"
+  mv -f config/autoconf.mk.orig config/autoconf.mk 2> /dev/null
+else
+  rm -f config/autoconf.mk.orig 2> /dev/null
+fi

old mode 100644
new mode 100755

--- a/js/src/configure.in
+++ b/js/src/configure.in
@@ -5294,14 +5294,24 @@ echo $MAKEFILES | ${PERL} $srcdir/build/
 else
 echo $MAKEFILES | ${PERL} $srcdir/build/autoconf/acoutput-fast.pl -nowrap --cygwin-srcdir=$srcdir > conftest.sh
 fi
 . ./conftest.sh
 rm conftest.sh
 
 echo $MAKEFILES > unallmakefiles
 
+mv -f config/autoconf.mk config/autoconf.mk.orig 2> /dev/null
+
 AC_OUTPUT($MAKEFILES)
 
+dnl Prevent the regeneration of autoconf.mk forcing rebuilds of the world
+if cmp -s config/autoconf.mk config/autoconf.mk.orig; then
+  echo "config/autoconf.mk is unchanged"
+  mv -f config/autoconf.mk.orig config/autoconf.mk 2> /dev/null
+else
+  rm -f config/autoconf.mk.orig 2> /dev/null
+fi
+
 # Produce the js-config script at configure time; see the comments for
 # 'js-config' in Makefile.in.
 AC_MSG_RESULT(invoking make to create js-config script)
 $MAKE js-config