diff --git a/firefox/40-no_proxy.yml b/firefox/40-no_proxy.yml
index bea2d81e..e76cd0ef 100644
--- a/firefox/40-no_proxy.yml
+++ b/firefox/40-no_proxy.yml
@@ -8,6 +8,7 @@ no_proxy:
     allow_without_dot: true
     allow_startswith_dot: true
   multi: true
+  mandatory: false
   disabled:
     variable: _.proxy_mode
     when: No proxy