Examine source code of Twitcasting-Shortcut

{
  "manifest_version": 2,
  "name": "Twitcasting-Shortcut",
  "version": "1.1",
  "description": "Add shortcut to send comment by Ctrl + Enter",
  "icons": {
    "48": "icons/icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{039506c0-da43-48ee-81c2-c771d1df5661}",
      "strict_min_version": "79.0"
    }
  },
  "content_scripts": [
    {
      "matches": [
        "https://twitcasting.tv/*"
      ],
      "js": [
        "sendComment.js"
      ]
    }
  ]
}