Examine source code of Clean Username

{
  "manifest_version": 2,
  "name": "Clean Username",
  "version": "0.0.1",
  "description": "Makes usernames in social-media appear in monotone",
  "content_scripts": [
    {
      "matches": [
        "*://twitter.com/*"
      ],
      "js": [
        "mono-user.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{02f056ce-90e9-4d8b-8fa5-2fc70c36abaa}"
    }
  }
}