diff --git a/4.1-Extensions.md b/4.1-Extensions.md
index c311d89..2febbe1 100644
--- a/4.1-Extensions.md
+++ b/4.1-Extensions.md
@@ -35,6 +35,9 @@ These are all, where applicable, best configured to `deny-all` and whitelist.
    * [FF59+](https://bugzilla.mozilla.org/show_bug.cgi?id=1381197) fixes incompatibility with FPI (privacy.firstparty.isolate)
    * unresolved: clearing IndexedDB by host
    * unknown: clearing service workers cache, appCache by host
+* [Temporary Containers](https://addons.mozilla.org/en-US/firefox/addon/temporary-containers/) <sup>✔ Privacy (stated on AMO)</sup> | [GitHub](https://github.com/stoically/temporary-containers)
+   * This can achieve *almost* everything First Party Isolation (FPI) does without breaking cross-domain logins
+   * In an hardened setup, this can even isolate repeat visits to the same domain, which FPI alone cannot.
 
 <sup>1</sup> Note: There are Web Extension API limitations, such as handling strict CSP and @run-at document-start. So TEST your scripts!