Examine source code of Serenity..

{
  "theme": {
    "images": {
      "theme_frame": "SerenityH.jpg"
    },
    "colors": {
      "frame": "#b0aaaa",
      "tab_background_text": "#000000"
    }
  },
  "version": "2.0",
  "name": "Serenity..",
  "manifest_version": 2,
  "description": "birds , lake, trees, plants, serene, flowers, clouds, reflection, My wallpaper to match can be found at: <a href=\"https://outgoing.prod.mozaws.net/v1/c6e042458bdee762f4d8969b03b5b8aabb39f2dd481b90588823eac79966d883/http%3A//nature.desktopnexus.com/wallpaper/694585/\" rel=\"nofollow\">http://nature.desktopnexus.com/wallpaper/694585/</a>"
}