Examine source code of Carte Postale

{
  "theme": {
    "images": {
      "theme_frame": "cartepostale.jpg"
    },
    "colors": {
      "frame": "#fffed5",
      "tab_background_text": "#000000"
    }
  },
  "version": "2.0",
  "name": "Carte Postale",
  "manifest_version": 2,
  "description": "Just a collection of old French postcards turned into a theme for your FireFox.  Enjoy!"
}