--- a/configure.ac
+++ b/configure.ac_new
@@ -87,16 +87,23 @@
 
 	if test "x${oldxul}" != xyes ; then
 
-		AC_MSG_CHECKING(Mozilla XPCOM > 1.8)
-		mozilla_xpcom_pcs="libxul-embedding-unstable"
-		for pc in $mozilla_xpcom_pcs; do
-			if $PKG_CONFIG --exists $pc; then
-				AC_MSG_RESULT($pc)
-				mozilla_xpcom=$pc
-				XUL_VERSION=3
-				break;
-			fi
-		done
+		if test -z $mozilla_xpcom; then
+			AC_MSG_CHECKING(Mozilla XPCOM > 1.8)
+			mozilla_xpcom_pcs="libxul-embedding libxul-embedding-unstable"
+			for pc in $mozilla_xpcom_pcs; do
+				if $PKG_CONFIG --exists $pc; then
+					mozilla_xpcom=$pc
+					XUL_VERSION=3
+					version="$(pkg-config --modversion $pc)"
+					minor=`echo "$version" | sed -e 's,\([[0-9]]*\)\..*,\1,'`
+					if test $minor -ge 2; then
+						XUL_VERSION=4
+					fi
+					AC_MSG_RESULT(Found $version)
+					break;
+				fi
+			done
+		fi
 	fi
 
 	if test -z $mozilla_xpcom; then
@@ -121,9 +128,12 @@
 	XPCOM_PKGS="$mozilla_xpcom"
 fi
 
-AM_CONDITIONAL([OLDXUL], [test x$XUL_VERSION = x2])
-
 AC_SUBST(XUL_VERSION)
+
+AM_CONDITIONAL([XUL_4], [test x$XUL_VERSION = x4])
+AM_CONDITIONAL([XUL_3], [test x$XUL_VERSION = x3])
+AM_CONDITIONAL([XUL_2], [test x$XUL_VERSION = x2])
+
 
 AC_ARG_ENABLE([optimize],
 	AC_HELP_STRING([--enable-optimize], [Enable optimizations (-O2)]),