Examine source code of GitHub Wider Sidebar

{
  "manifest_version": 2,
  "name": "GitHub Wider Sidebar",
  "version": "2.0",
  "description": "Makes GitHub's sidebar wider",
  "permissions": [
    "*://github.com/*"
  ],
  "content_scripts": [
    {
      "matches": [
        "*://github.com/*"
      ],
      "css": [
        "styles.css"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "wider-sidebar@yourdomain.com"
    }
  }
}