Examine source code of Zombie Horde

{
  "theme": {
    "images": {
      "theme_frame": "FirefoxPersona-ZombieHordeHeader.jpg"
    },
    "colors": {
      "frame": "rgba(229,230,232,1)",
      "tab_background_text": "#33de67"
    }
  },
  "version": "2.0",
  "name": "Zombie Horde",
  "manifest_version": 2,
  "description": "Zombie Horde swarms over your Firefox browser with the \"way too red\" background and ghouls from the Year Of The Zombie calendar art. Keep on Zombing!"
}