--- a/build/moz.configure/old.configure
+++ b/build/moz.configure/old.configure
@@ -331,17 +331,16 @@ def old_configure_options(*options):
     '--with-google-api-keyfile',
     '--with-google-oauth-api-keyfile',
     '--with-gradle',
     '--with-intl-api',
     '--with-ios-sdk',
     '--with-java-bin-path',
     '--with-jitreport-granularity',
     '--with-l10n-base',
-    '--with-libxul-sdk',
     '--with-linux-headers',
     '--with-macbundlename-prefix',
     '--with-macos-private-frameworks',
     '--with-macos-sdk',
     '--with-mozilla-api-keyfile',
     '--with-nspr-prefix',
     '--with-nspr-cflags',
     '--with-nspr-libs',

--- a/old-configure.in
+++ b/old-configure.in
@@ -2684,20 +2684,16 @@ dnl are defined in build/autoconf/altopt
 
 dnl ========================================================
 dnl =
 dnl = Check for external package dependencies
 dnl =
 dnl ========================================================
 MOZ_ARG_HEADER(External Packages)
 
-MOZ_ARG_WITH_STRING(libxul-sdk,
-[  --with-libxul-sdk=PFX   Use the libXUL SDK at <PFX>],
-  AC_MSG_ERROR([--with-libxul-sdk is not supported anymore.]))
-
 case "$OS_TARGET" in
 WINNT|Darwin|Android)
   MOZ_FOLD_LIBS=1
   ;;
 *)
   MOZ_FOLD_LIBS=
   ;;
 esac