diff -ruN /usr/ports/www/firefox/Makefile firefox/Makefile
--- /usr/ports/www/firefox/Makefile	2012-06-18 22:45:40.000000000 -0500
+++ firefox/Makefile	2012-06-18 22:49:20.000000000 -0500
@@ -60,6 +60,8 @@
 
 .if empty(CXX:M*clang++*) && ${OSVERSION} > 900000
 USE_GCC=	4.6+
+.else
+CFLAGS+=	-mmmx
 .endif
 
 WRKSRC:=	${WRKDIR}/mozilla-release