diff --git a/how-to-mitigate-fingerprinting-and-ip-leaks-using-firefox-advanced-preferences/README.md b/how-to-mitigate-fingerprinting-and-ip-leaks-using-firefox-advanced-preferences/README.md
index 4da006f..66617f0 100644
--- a/how-to-mitigate-fingerprinting-and-ip-leaks-using-firefox-advanced-preferences/README.md
+++ b/how-to-mitigate-fingerprinting-and-ip-leaks-using-firefox-advanced-preferences/README.md
@@ -35,6 +35,7 @@ network.http.sendRefererHeader = 0
 network.prefetch-next = false
 privacy.firstparty.isolate = true
 privacy.resistFingerprinting = true
+privacy.resistFingerprinting.letterboxing = true
 privacy.trackingprotection.enabled = true
 webgl.disabled =  true
 ```