Firefox 扩展中未加载 Javascript Fetch API

如何解决Firefox 扩展中未加载 Javascript Fetch API

Javascript Fetch API 未加载到 Firefox 扩展中。我是一个安静的新人，但我该如何解决这个问题，或者我必须在浏览器扩展中从服务器获取文件的替代方法？

test.html

<!DOCTYPE html>
<html>
<body>
<p id="demo">Fetch a file to change this text.</p>
<script>


fetch ('http://localhost/test/test.txt')
.then(x => x.text())
.then(y => document.getElementById("demo").innerHTML = y);

</script>
</body>
</html>

manifest.json

{

  "manifest_version": 2,"name": "test","version": "1","description": "test","permissions": [
    "storage","activeTab","tabs","http://*/*","https://*/*"
  ],"browser_action": {
   
    "default_title": "test","default_popup": "popup/test.html"
  }
}