Examine source code of Matera

{
  "theme": {
    "images": {
      "theme_frame": "tema_firefox1.jpg"
    },
    "colors": {
      "frame": "#2ee8dc",
      "tab_background_text": "#261f1f"
    }
  },
  "version": "2.0",
  "name": "Matera",
  "manifest_version": 2,
  "description": "Matera is one of the most ancient town in the world because of continual presence of mankind from paleolitic age up to present time. Since 1993 is preserved by UNESCO."
}