Examine source code of WebGrader

{
  "manifest_version": 2,
  "name": "WebGrader",
  "version": "5.0",
  "author": "Nik Grebovšek",
  "description": "With this Extension you can grade websites.",
  "icons": {
    "48": "icons/icon48.png"
  },
  "browser_action": {
    "browser_style": true,
    "default_popup": "popup/index.html",
    "default_icon": {
      "32": "icons/icon.png"
    }
  },
  "permissions": [
    "tabs"
  ],
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": true
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{c9fb3096-b460-426d-9ac8-3c6c66318200}"
    }
  }
}