Examine source code of Snow

{
  "name": "Snow",
  "description": "Snow on pages",
  "version": "0.0.1",
  "manifest_version": 2,
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "snow.js"
      ],
      "css": [
        "snow.css"
      ]
    }
  ],
  "icons": {
    "48": "icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{b1ff5460-64b9-4a1d-8570-f6c2e5892bce}"
    }
  }
}