Examine source code of Fog for Firefox

{
  "manifest_version": 2,
  "name": "Fog for Firefox",
  "version": "1.0",
  "description": "Adds fog to Firefox, to make it harder to see and use.",
  "icons": {
    "48": "icons/icon_48.png"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "fog.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{a0e7deed-0024-4e44-ba6d-49950802da75}"
    }
  }
}