diff --git a/config.def.h b/config.def.h
index 8347e07..41efe3e 100644
--- a/config.def.h
+++ b/config.def.h
@@ -28,6 +28,7 @@ static const Rule rules[] = {
 	 */
 	/* class      instance    title       tags mask     isfloating   monitor */
 	{ "Gimp",     NULL,       NULL,       0,            1,           -1 },
+	{ "Firefox",  NULL,       NULL,       0,            0,           -1 },
 };
 
 /* layout(s) */