--- a/config/autoconf.mk.in
+++ b/config/autoconf.mk.in
@@ -39,16 +39,18 @@
 # A netscape style .mk file for autoconf builds
 
 INCLUDED_AUTOCONF_MK = 1
 USE_AUTOCONF 	= 1
 MOZILLA_CLIENT	= 1
 COMM_BUILD = @COMM_BUILD@
 MOZILLA_SRCDIR = @MOZILLA_SRCDIR@
 MOZILLA_VERSION = @MOZILLA_VERSION@
+MOZILLA_1_9_1_BRANCH = @MOZILLA_1_9_1_BRANCH@
+
 THUNDERBIRD_VERSION	= @THUNDERBIRD_VERSION@
 SUNBIRD_VERSION = @SUNBIRD_VERSION@
 SEAMONKEY_VERSION	= @SEAMONKEY_VERSION@
 
 MOZ_BUILD_APP = @MOZ_BUILD_APP@
 MOZ_APP_NAME	= @MOZ_APP_NAME@
 MOZ_APP_DISPLAYNAME = @MOZ_APP_DISPLAYNAME@
 MOZ_APP_VERSION = @MOZ_APP_VERSION@

--- a/configure.in
+++ b/configure.in
@@ -1588,16 +1588,28 @@ case "$host" in
     HOST_CFLAGS="$HOST_CFLAGS -DXP_UNIX"
     HOST_OPTIMIZE_FLAGS="${HOST_OPTIMIZE_FLAGS=-O2}"
     ;;
 esac
 
 dnl Get mozilla version from central milestone file
 MOZILLA_VERSION=`$PERL $MOZILLA_SRCDIR/config/milestone.pl -topsrcdir $MOZILLA_SRCDIR`
 
+changequote(,)
+MOZILLA_BRANCH_VERSION=`echo ${MOZILLA_VERSION} | sed -e 's/\(^[0-9]\.[0-9]\.[0-9]\).*/\1/;'`
+changequote([,])
+
+MOZILLA_1_9_1_BRANCH=
+
+if test "$MOZILLA_BRANCH_VERSION" = "1.9.1"; then
+    MOZILLA_1_9_1_BRANCH=1
+fi
+
+AC_SUBST(MOZILLA_1_9_1_BRANCH)
+
 dnl Get version of various core apps from the version files.
 THUNDERBIRD_VERSION=`cat $topsrcdir/mail/config/version.txt`
 SUNBIRD_VERSION=`cat $topsrcdir/calendar/sunbird/config/version.txt`
 SEAMONKEY_VERSION=`cat $topsrcdir/suite/config/version.txt`
 
 AC_DEFINE_UNQUOTED(MOZILLA_VERSION,"$MOZILLA_VERSION")
 AC_DEFINE_UNQUOTED(MOZILLA_VERSION_U,$MOZILLA_VERSION)