Examine source code of hubser.de - Official

{
  "theme": {
    "images": {
      "theme_frame": "header.png"
    },
    "colors": {
      "frame": "rgba(229,230,232,1)",
      "tab_background_text": "#000"
    }
  },
  "version": "2.0",
  "name": "hubser.de - Official",
  "manifest_version": 2,
  "description": "The official <a rel=\"nofollow\" href=\"https://outgoing.prod.mozaws.net/v1/bc93d933dd62ff9c46a4809d6dbc356799828425284a80664263ff0694efdda5/http%3A//hubser.de\">hubser.de</a>-Theme for Mozilla's open source browser Firefox."
}