diff --git a/platform/mv3/extension/js/scripting-manager.js b/platform/mv3/extension/js/scripting-manager.js
index c90b942a4..65ea39974 100644
--- a/platform/mv3/extension/js/scripting-manager.js
+++ b/platform/mv3/extension/js/scripting-manager.js
@@ -34,6 +34,8 @@ import * as ut from './utils.js';
 
 /******************************************************************************/
 
+const isGecko = browser.runtime.getURL('').startsWith('moz-extension://');
+
 const resourceDetailPromises = new Map();
 
 function getSpecificDetails() {
@@ -355,7 +357,7 @@ function registerDeclarative(context, declarativeDetails) {
 function registerScriptlet(context, scriptletDetails) {
     // https://bugzilla.mozilla.org/show_bug.cgi?id=1736575
     //   `MAIN` world not yet supported in Firefox
-    if ( navigator && navigator.product === 'Gecko' ) { return; }
+    if ( isGecko ) { return; }
 
     const { before, filteringModeDetails, rulesetsDetails } = context;
 
@@ -433,7 +435,7 @@ function registerScriptlet(context, scriptletDetails) {
 function registerScriptletEntity(context) {
     // https://bugzilla.mozilla.org/show_bug.cgi?id=1736575
     //   `MAIN` world not yet supported in Firefox
-    if ( navigator && navigator.product === 'Gecko' ) { return; }
+    if ( isGecko ) { return; }
 
     const { before, filteringModeDetails, rulesetsDetails } = context;