Examine source code of Metal X

{
  "theme": {
    "images": {
      "theme_frame": "header.png"
    },
    "colors": {
      "frame": "#000000",
      "tab_background_text": "#ffffff"
    }
  },
  "version": "2.0",
  "name": "Metal X",
  "manifest_version": 2,
  "description": "Stock image: <a rel=\"nofollow\" href=\"https://outgoing.prod.mozaws.net/v1/91527f033edbb6377838b8bc2e82622b3ea8e6b2b30c48a305a86678aa2bb736/http%3A//www.freepik.com/\">http://www.freepik.com/</a>"
}