Examine source code of Grain mania

{
  "theme": {
    "images": {
      "theme_frame": "firefox_header_background.jpg"
    },
    "colors": {
      "frame": "#c9c9c9",
      "tab_background_text": "#000000"
    }
  },
  "version": "2.0",
  "name": "Grain mania",
  "manifest_version": 2,
  "description": "Simple persona, base on one photo."
}