diff --git a/firefox/30-auto.yml b/firefox/30-auto.yml
index e31729a..130fae0 100644
--- a/firefox/30-auto.yml
+++ b/firefox/30-auto.yml
@@ -2,3 +2,6 @@
 auto:
   description: Automatic proxy configuration URL
   type: web_address
+  disabled:
+    variable: proxy_mode
+    when_not: Automatic proxy configuration URL