diff --git a/4.1-Extensions.md b/4.1-Extensions.md
index 2343afc..b5d54f4 100644
--- a/4.1-Extensions.md
+++ b/4.1-Extensions.md
@@ -15,6 +15,7 @@ These are all, where applicable, best configured to `deny-all` and whitelist.
 * [uMatrix](https://addons.mozilla.org/firefox/addon/umatrix/) <sup>✔ [Privacy](https://github.com/gorhill/uMatrix/wiki/Privacy-policy)</sup> | [GitHub](https://github.com/gorhill/uMatrix)
 * [CanvasBlocker](https://addons.mozilla.org/firefox/addon/canvasblocker/) <sup>✔ [Privacy](https://addons.mozilla.org/firefox/addon/canvasblocker/privacy/)</sup> | [GitHub](https://github.com/kkapsner/CanvasBlocker)
 * [Decentraleyes](https://addons.mozilla.org/firefox/addon/decentraleyes/) <sup>✔ [Privacy](https://addons.mozilla.org/firefox/addon/decentraleyes/privacy/)</sup> | [GitHub](https://github.com/Synzvato/decentraleyes)
+* [CSS Exfil Protection](https://addons.mozilla.org/firefox/addon/css-exfil-protection/) | [Homepage/Tests](https://www.mike-gualtieri.com/css-exfil-vulnerability-tester)
 * [HTTPS Everywhere](https://addons.mozilla.org/firefox/addon/https-everywhere/) <sup>✔ [Privacy](https://www.eff.org/code/privacy/policy)</sup> | [GitHub](https://github.com/EFForg/https-everywhere)
 * [Smart Referer](https://addons.mozilla.org/firefox/addon/smart-referer/) | [GitHub](https://github.com/meh/smart-referer)
 * [Header Editor](https://addons.mozilla.org/firefox/addon/header-editor/) | [GitHub](https://github.com/FirefoxBar/HeaderEditor)