Examine source code of Dancing Alien

{
  "manifest_version": 2,
  "name": "Dancing Alien",
  "version": "1.0",
  "description": "Adds a dancing Alien to the corner of the screen",
  "icons": {
    "48": "icons/dancingBicho.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.mozilla.org/*"
      ],
      "js": [
        "index.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{7560c47b-ef8f-4dd8-a64c-4bf924b09ca6}"
    }
  }
}