Examine source code of Metafields Guru

{
  "manifest_version": 2,
  "name": "Metafields Guru",
  "author": "256 Development",
  "version": "3.11.0",
  "description": "Bring metafields management to a new level.",
  "icons": {
    "16": "icons/16.png",
    "48": "icons/48.png",
    "128": "icons/128.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.myshopify.com/admin/*",
        "*://support.metafields.guru/",
        "https://admin.shopify.com/*"
      ],
      "js": [
        "content.js"
      ]
    }
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_title": "Metafields Guru",
    "default_popup": "popup.html"
  },
  "permissions": [
    "tabs",
    "storage",
    "*://*.myshopify.com/admin/*",
    "*://app.metafields.guru/*",
    "*://support.metafields.guru/*",
    "*://admin.shopify.com/*",
    "*://*.googleapis.com/*"
  ],
  "web_accessible_resources": [
    "content.css"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{05868732-8544-4734-8007-1900a24c05c0}"
    }
  }
}