Examine source code of AppelSummer

{
  "theme": {
    "images": {
      "theme_frame": "firefox_head-appel.jpg"
    },
    "colors": {
      "frame": "#8c8888",
      "tab_background_text": "#000000"
    }
  },
  "version": "2.0",
  "name": "AppelSummer",
  "manifest_version": 2,
  "description": "Apfel, Appel, Sommer, Summer, Sonne, Sun,"
}