Examine source code of Leetcode FRIENDS

{
  "manifest_version": 3,
  "name": "Leetcode FRIENDS",
  "version": "1.1",
  "description": "leetcode extension to store friends username",
  "icons": {
    "48": "leetcode.svg"
  },
  "permissions": [
    "storage"
  ],
  "action": {
    "default_popup": "index.html",
    "default_icon": "./leetcode.ico"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "leetcode@leftover.com"
    }
  }
}