Disable test from bug 393970 on linux (bug 428226)

layout/xul/base/test/Makefile.in

@@ -44,11 +44,10 @@ relativesrcdir  = layout/xul/base/test
 include $(DEPTH)/config/autoconf.mk
 include $(topsrcdir)/config/rules.mk
 
-_TEST_FILES = 	$(NULL)
-
 ifneq ($(OS_ARCH),Linux)
-_TEST_FILES += test_bug393970.xul
-endif
+_TEST_FILES = 	test_bug393970.xul \
+		$(NULL)
 
 libs:: $(_TEST_FILES)
 	$(INSTALL) $^ $(DEPTH)/_tests/testing/mochitest/tests/$(relativesrcdir)
+endif