--- a/old-configure.in
+++ b/old-configure.in
@@ -3949,26 +3949,16 @@ MOZ_ARG_ENABLE_BOOL(reflow-perf,
 [  --enable-reflow-perf    Enable reflow performance tracing],
     MOZ_REFLOW_PERF=1,
     MOZ_REFLOW_PERF= )
 if test -n "$MOZ_REFLOW_PERF"; then
     AC_DEFINE(MOZ_REFLOW_PERF)
 fi
 
 dnl ========================================================
-dnl = Horizon build options - set default preferences for
-dnl   the horizon project. Horizon is a browser built on
-dnl   top of the graphene runtime.
-dnl ========================================================
-if test -n "$MOZ_HORIZON"; then
-    AC_DEFINE(MOZ_HORIZON)
-fi
-AC_SUBST(MOZ_HORIZON)
-
-dnl ========================================================
 dnl = Offer a way to disable the startup cache
 dnl ========================================================
 
 MOZ_ARG_DISABLE_BOOL(startupcache,
 [  --disable-startupcache          Disable startup cache ],
     MOZ_DISABLE_STARTUPCACHE=1,
     MOZ_DISABLE_STARTUPCACHE=)