--- a/eclass/mozconfig-3.eclass	
+++ a/eclass/mozconfig-3.eclass	
@@ -34,6 +34,9 @@ mozconfig_config() {
 
 	if has bindist ${IUSE}; then
 		mozconfig_use_enable !bindist official-branding
+		if [[ ${PN} == firefox ]] ; then
+			mozconfig_annotate '+bindist' --with-branding="browser/branding/unofficial"
+		fi
 	fi
 
 	mozconfig_use_enable alsa ogg