diff --git a/user.js b/user.js
index cfbb273..a7728ba 100644
--- a/user.js
+++ b/user.js
@@ -1377,6 +1377,10 @@ user_pref("privacy.firstparty.isolate", true);
  * [3] https://developer.mozilla.org/en-US/docs/Web/API/Window/postMessage ***/
    // user_pref("privacy.firstparty.isolate.restrict_opener_access", true); // [DEFAULT: true]
    // user_pref("privacy.firstparty.isolate.block_post_message", true);
+/* 4003: enable scheme with FPI [FF78+]
+ * [NOTE] Experimental: existing data and site permissions are incompatible
+ * and some site exceptions may not work e.g. HTTPS-only mode (see 1244) ***/
+   // user_pref("privacy.firstparty.isolate.use_site", true);
 
 /*** [SECTION 4500]: RFP (RESIST FINGERPRINTING)
    RFP covers a wide range of ongoing fingerprinting solutions.