Examine source code of Metropolis Dark

{
  "theme": {
    "images": {
      "theme_frame": "Firefox_persona_header7.jpg"
    },
    "colors": {
      "frame": "#878787",
      "tab_background_text": "#878787"
    }
  },
  "version": "2.0",
  "name": "Metropolis Dark",
  "manifest_version": 2,
  "description": "<a href=\"https://outgoing.prod.mozaws.net/v1/1d7dbcaa61d2decaa61bf705693f6e93a96d78deeb7a9aa72d1adf3da0497ec3/http%3A//www.metropoliscreative.com\" rel=\"nofollow\">http://www.metropoliscreative.com</a>"
}