Examine source code of Firefox Horizon

{
  "theme": {
    "images": {
      "theme_frame": "header.png"
    },
    "colors": {
      "frame": "#ffffff",
      "tab_background_text": "#000000"
    }
  },
  "version": "2.0",
  "name": "Firefox Horizon",
  "manifest_version": 2,
  "description": "I really like this picture and wanted it as a theme, but could not find it. I am unaware of who the artist is, but it is the picture you see when you got to the download page of Firefox. If anyone knows the artist let me know so I can credit them.\nThis is my first attempt and I hope you enjoy."
}