diff --git a/config/mozilla.cfg b/config/mozilla.cfg
index e5d5206..2709f2f 100644
--- a/config/mozilla.cfg
+++ b/config/mozilla.cfg
@@ -888,7 +888,7 @@ lockPref("network.http.referer.spoofSource", true); // [DEFAULT: false]
 lockPref("security.dialog_enable_delay", 1000); // [DEFAULT: 1000]
 // -------------------------------------
 // Enforce no First Party Isolation [FF51+]
-defaultPref("privacy.firstparty.isolate", false); // [DEFAULT: false]
+defaultPref("privacy.firstparty.isolate", true); // [DEFAULT: false]
 // -------------------------------------
 // Enforce SmartBlock shims (about:compat) [FF81+]
 lockPref("extensions.webcompat.enable_shims", true); // [HIDDEN PREF] [DEFAULT: true]