Examine source code of Give A Spark

{
  "manifest_version": 2,
  "name": "Give A Spark",
  "description": "Give A Spark is an email signature tool through which you can set your email signature on different emails.",
  "version": "1.1",
  "browser_action": {
    "default_popup": "popup.html"
  },
  "permissions": [
    "cookies",
    "https://api.giveaspark.com/*",
    "https://giveaspark.s3.us-west-1.amazonaws.com/*",
    "https://outlook.live.com/*",
    "https://mail.yahoo.com/*",
    "https://mail.yandex.com/*"
  ],
  "content_scripts": [
    {
      "matches": [
        "https://outlook.live.com/*",
        "https://mail.yahoo.com/*",
        "https://mail.yandex.com/*"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_end"
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{a232dd1b-db6b-4cc9-bb84-1a8c5749bf76}"
    }
  }
}