app/assets/javascripts/decidim/forms/forms.js.es6 in decidim-forms-0.23.6 vs app/assets/javascripts/decidim/forms/forms.js.es6 in decidim-forms-0.24.0.rc1

@@ -51,18 +51,18 @@
     });
     $(document).on("submit", "form", (event) => {
       window.exitUrl = event.currentTarget.action;
     });
 
-    window.onbeforeunload = () => {
+    window.addEventListener("beforeunload", (event) => {
       const exitUrl = window.exitUrl;
       const hasChanged = $form.data("changed");
       window.exitUrl = null;
 
       if (!hasChanged || (exitUrl && exitUrl.includes(safePath))) {
-        return null;
+        return;
       }
 
-      return "";
-    }
+      event.returnValue = true;
+    });
   }
 })(window);