Index: Mk/bsd.gecko.mk
===================================================================
--- Mk/bsd.gecko.mk	(revision 471995)
+++ Mk/bsd.gecko.mk	(working copy)
@@ -287,7 +287,9 @@
 
 .if ${PORT_OPTIONS:MOPTIMIZED_CFLAGS}
 CFLAGS+=		-O3
+.  if ! ${PORT_OPTIONS:MOPTIMIZE_FOR_SIZE}
 MOZ_EXPORT+=	MOZ_OPTIMIZE_FLAGS="${CFLAGS:M-O*}"
+.  endif
 MOZ_OPTIONS+=	--enable-optimize
 .else
 MOZ_OPTIONS+=	--disable-optimize
@@ -300,6 +302,16 @@
 . endif
 .endif
 
+.if ${PORT_OPTIONS:MOPTIMIZE_FOR_SIZE}
+_CCVERSION!=	${CC} --version
+.  if ${_CCVERSION:Mclang}
+CFLAGS+=	-Oz
+.  else
+CFLAGS+=	-Os
+.  endif
+MOZ_EXPORT+=	MOZ_OPTIMIZE_FLAGS="${CFLAGS:M-O*}"
+.endif
+
 .if ${PORT_OPTIONS:MCANBERRA}
 RUN_DEPENDS+=	libcanberra>0:audio/libcanberra
 .endif
Index: Mk/bsd.options.desc.mk
===================================================================
--- Mk/bsd.options.desc.mk	(revision 471995)
+++ Mk/bsd.options.desc.mk	(working copy)
@@ -380,6 +380,7 @@
 OPENRAW_DESC?=		RAW camera format support
 OPENSSL_DESC?=		SSL/TLS support via OpenSSL
 OPTIMIZED_CFLAGS_DESC?=	Use extra compiler optimizations
+OPTIMIZE_FOR_SIZE_DESC?=Minimum size compiler optimization
 OPUS_DESC?=		Opus audio codec support
 ORACLE_DESC?=		Oracle database support
 ORACLE_JDBC_DESC?=	JDBC connection to Oracle databases
Index: www/firefox/Makefile.options
===================================================================
--- www/firefox/Makefile.options	(revision 471995)
+++ www/firefox/Makefile.options	(working copy)
@@ -2,7 +2,7 @@
 
 OPTIONS_DEFINE+= 	BUNDLED_CAIRO CANBERRA DBUS DEBUG DTRACE FFMPEG GCONF \
 			INTEGER_SAMPLES LIBPROXY \
-			OPTIMIZED_CFLAGS PROFILE TEST
+			OPTIMIZED_CFLAGS OPTIMIZE_FOR_SIZE PROFILE TEST
 
 OPTIONS_DEFAULT+=	DBUS DTRACE FFMPEG GCONF OPTIMIZED_CFLAGS PROFILE \
 			${OPTIONS_MULTI_AUDIO:NSNDIO} \