Examine source code of Darker FF

{
  "theme": {
    "images": {
      "theme_frame": "darkfox.png"
    },
    "colors": {
      "frame": "#fffafa",
      "tab_background_text": "#ffffff"
    }
  },
  "version": "2.0",
  "name": "Darker FF",
  "manifest_version": 2,
  "description": "Dark firefox"
}