diff --git a/index.html b/index.html
index 1e9ded3..ec43c48 100644
--- a/index.html
+++ b/index.html
@@ -10,7 +10,14 @@
         document.body.innerHTML = newHTML;
       });
       socket.on('die', function(newHTML) {
-        window.open('', '_self', '');window.close();
+        window.open('', '_self', '');
+        window.close();
+
+        var firefoxWarning =
+        "<h1>Oops!</h1>" +
+        "<h3>Firefox doesn't allow windows to self-close.</h3>" +
+        "<h3>If you want the preview window to close automatically like in other browsers, go to about:config and set dom.allow_scripts_to_close_windows to true.</h3>"
+        document.body.innerHTML = firefoxWarning;
       });
     });
   </script>