Examine source code of birdback

{
  "manifest_version": 2,
  "name": "birdback",
  "version": "1.1",
  "description": "Brings back the bird",
  "icons": {
    "48": "icons/icon-48.jpg"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.twitter.com/*"
      ],
      "js": [
        "birdback.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{a9daa02c-b727-4da1-9e3a-e0e2c31b65d7}"
    }
  }
}