diff --git a/firefox-jenkins-slave/README.md b/firefox-jenkins-slave/README.md
index 76b2aa6..1a8194f 100644
--- a/firefox-jenkins-slave/README.md
+++ b/firefox-jenkins-slave/README.md
@@ -2,11 +2,19 @@ Complete image to run Jenkins as a slave with headless Firefox
 ==============================================================
 
 Installed are:
+
 - Supervisord (inherited)
 - Oracle Java 7 Development Kit (inherited)
 - Firefox
 - Xvfb headless display driver
 
+Run a headless process
+----------------------
+
+Run your script, but first do
+
+    export DISPLAY=:10
+
 Run with access to Docker on the host
 -------------------------------------