diff --git a/Optional-Hardening.md b/Optional-Hardening.md
index a6cc154..23a4865 100644
--- a/Optional-Hardening.md
+++ b/Optional-Hardening.md
@@ -118,6 +118,19 @@ user_pref("default-browser-agent.enabled", false);
 
 ***
 
+### Public Key Pinning
+[Public Key Pinning](https://wiki.mozilla.org/SecurityEngineering/Public_Key_Pinning) (PKP) is a tool that boosts the safety of [SSL certificates](https://www.cloudflare.com/learning/ssl/what-is-an-ssl-certificate/) by linking a website to its unique security key. This process ensures that the website you're visiting is real and not fake. PKP stops any attempts to trick your computer into connecting with a fraudulent website.
+
+:warning: Sometimes antivirus software — or some other [source](https://github.com/yokoffing/Betterfox/issues/232#issuecomment-1732346856) — won't let you open websites ([example](https://www.reddit.com/r/firefox/comments/16mlv15/kaspersky_cant_scan_encrypted_connections_with/)).
+
+```
+// PREF: enforce certificate pinning
+// [ERROR] MOZILLA_PKIX_ERROR_KEY_PINNING_FAILURE
+user_pref("security.cert_pinning.enforcement_level", 2);
+```
+
+***
+
 ### Require Safe Negotiation
 
 :warning: Some sites, like `EA.com`, will not let you login due to their weak encryption.