Examine source code of Group Leads

{
  "applications": {
    "gecko": {
      "id": "addon@groupleads.net"
    }
  },
  "manifest_version": 2,
  "name": "Group Leads",
  "short_name": "Group Leads",
  "version": "1.3.5",
  "description": "Group leads helps you to instantly convert new facebook group members into leads in your favorite email marketing software.",
  "background": {
    "scripts": [
      "/assets/lib/jquery-3.5.1.min.js",
      "/assets/lib/moment.min.js",
      "/config.js",
      "/assets/js/background.js",
      "/background/authorize.js"
    ]
  },
  "icons": {
    "16": "icon16.png",
    "32": "icon32.png",
    "128": "icon128.png"
  },
  "browser_action": {
    "browser_style": false,
    "default_title": "Group Leads",
    "default_popup": "/index.html"
  },
  "permissions": [
    "tabs",
    "*://*.facebook.com/*",
    "*://*.groupleads.net/*",
    "*://*.api-us1.com/*",
    "https://oauth2.googleapis.com/*",
    "storage",
    "cookies",
    "identity",
    "notifications",
    "*://*.google.com/*",
    "webRequest",
    "webRequestBlocking"
  ],
  "content_scripts": [
    {
      "matches": [
        "*://*.facebook.com/*"
      ],
      "js": [
        "/assets/lib/jquery-3.5.1.min.js",
        "/config.js",
        "/assets/js/formfiller.js",
        "/assets/js/autoapproveformfiller.js"
      ],
      "css": [
        "/assets/css/groupleads.css"
      ],
      "all_frames": true
    }
  ],
  "web_accessible_resources": [
    "icon32.png"
  ]
}