diff --git a/browser/brave_shields/ad_block_service_browsertest.cc b/browser/brave_shields/ad_block_service_browsertest.cc
index 30cd52b3cc18..41051d82aa84 100644
--- a/browser/brave_shields/ad_block_service_browsertest.cc
+++ b/browser/brave_shields/ad_block_service_browsertest.cc
@@ -2384,7 +2384,7 @@ IN_PROC_BROWSER_TEST_F(ScriptletDebugLogsFlagEnabledTest, CanDebugSetToTrue) {
   ASSERT_TRUE(InstallDefaultAdBlockExtension());
   std::string scriptlet =
       "(function() {"
-      "  if (scriptletGlobals.get('canDebug')) {"
+      "  if (scriptletGlobals.get('canDebug') && scriptletGlobals.canDebug) {"
       "    window.success = true;"
       "  }"
       "})();";
diff --git a/components/cosmetic_filters/renderer/cosmetic_filters_js_handler.cc b/components/cosmetic_filters/renderer/cosmetic_filters_js_handler.cc
index 248613378cfd..c460870e85d4 100644
--- a/components/cosmetic_filters/renderer/cosmetic_filters_js_handler.cc
+++ b/components/cosmetic_filters/renderer/cosmetic_filters_js_handler.cc
@@ -45,7 +45,7 @@ const char kObservingScriptletEntryPoint[] =
 
 const char kScriptletInitScript[] =
     R"((function() {
-          let text = '(function() {\nconst scriptletGlobals = new Map(%s);\nlet deAmpEnabled = %s;\n' + %s + '})()';
+          let text = '(function() {\nconst scriptletGlobals = (() => {\nconst forwardedMapMethods = ["has", "get", "set"];\nconst handler = {\nget(target, prop) { if (forwardedMapMethods.includes(prop)) { return Map.prototype[prop].bind(target) } return target.get(prop); },\nset(target, prop, value) { if (!forwardedMapMethods.includes(prop)) { target.set(prop, value); } }\n};\nreturn new Proxy(new Map(%s), handler);\n})();\nlet deAmpEnabled = %s;\n' + %s + '})()';
           let script;
           try {
             script = document.createElement('script');