diff --git a/packages/devtools/client/exports/mount.mjs b/packages/devtools/client/exports/mount.mjs
index f32dc0ab1546..daf3253269fa 100644
--- a/packages/devtools/client/exports/mount.mjs
+++ b/packages/devtools/client/exports/mount.mjs
@@ -1,45 +1,49 @@
-import { parseQuery } from 'ufo';
+/* WARNING: NO ES6 SYNTAX HERE!!! */
+/* eslint-disable no-inner-declarations */
+/* eslint-disable no-var */
 import routesManifest from '../dist/routes-manifest.json';
 
-/**
- * @param {import('@modern-js/devtools-kit').SetupClientOptions} options
- */
-const mountDevTools = options => {
-  const container = document.createElement('div');
-  container.className = '_modern_js_devtools_container';
-  document.body.appendChild(container);
+(function () {
+  /**
+   * @param {import('@modern-js/devtools-kit').SetupClientOptions} options
+   */
+  function mountDevTools(options) {
+    var container = document.createElement('div');
+    container.className = '_modern_js_devtools_container';
+    document.body.appendChild(container);
 
-  const shadow = container.attachShadow({ mode: 'closed' });
+    var shadow = container.attachShadow({ mode: 'closed' });
 
-  for (const asset of routesManifest.routeAssets.mount.assets) {
-    if (asset.endsWith('.js')) {
-      const el = document.createElement('script');
-      el.src = asset;
+    routesManifest.routeAssets.mount.assets.forEach(function (asset) {
+      var el;
+      if (asset.endsWith('.js')) {
+        el = document.createElement('script');
+        el.src = asset;
+      } else if (asset.endsWith('.css')) {
+        el = document.createElement('link');
+        el.href = asset;
+        el.rel = 'stylesheet';
+      }
       shadow.appendChild(el);
-    } else if (asset.endsWith('.css')) {
-      const el = document.createElement('link');
-      el.href = asset;
-      el.rel = 'stylesheet';
-      shadow.appendChild(el);
-    }
-  }
+    });
 
-  const app = document.createElement('div');
-  app.className = '_modern_js_devtools_mountpoint theme-register';
-  const appGlobalExport = `_modern_js_devtools_app`;
-  window[appGlobalExport] = {
-    container: app,
-    options,
-  };
-  shadow.appendChild(app);
-};
+    var app = document.createElement('div');
+    app.className = '_modern_js_devtools_mountpoint theme-register';
+    var appGlobalExport = `_modern_js_devtools_app`;
+    window[appGlobalExport] = {
+      container: app,
+      options,
+    };
+    shadow.appendChild(app);
+  }
 
-try {
-  // eslint-disable-next-line no-undef
-  const opts = parseQuery(__resourceQuery);
-  mountDevTools(opts);
-} catch (err) {
-  const e = new Error('Failed to execute mount point of DevTools.');
-  e.cause = err;
-  console.error(e);
-}
+  try {
+    // eslint-disable-next-line no-undef
+    var opts = decodeURIComponent(__resourceQuery);
+    mountDevTools(opts);
+  } catch (err) {
+    var e = new Error('Failed to execute mount point of DevTools.');
+    e.cause = err;
+    console.error(e);
+  }
+})();