Examine source code of Level 4

{
  "theme": {
    "images": {
      "theme_frame": "Untitled-2.jpg"
    },
    "colors": {
      "frame": "#ffaa00",
      "tab_background_text": "#125996"
    }
  },
  "version": "2.0",
  "name": "Level 4",
  "manifest_version": 2,
  "description": "The Level 4 webcomic's official Firefox persona."
}