Examine source code of Blue Feels

{
  "theme": {
    "images": {
      "theme_frame": "header.png"
    },
    "colors": {
      "frame": "rgba(229,230,232,1)",
      "tab_background_text": "#000"
    }
  },
  "version": "2.0",
  "name": "Blue Feels",
  "manifest_version": 2,
  "description": "Gentle blue background with white fade overlay.\n\nI was looking for mellow colors to use to differentiate between different open FF profile windows and couldn't find anything solid, light and unobtrusive. So I made these.  Hope you like them.\n\nIf you want to see more of my vector graphic work, check out <a rel=\"nofollow\" href=\"https://outgoing.prod.mozaws.net/v1/a92b5c4fbc5897ec0144e0c271fbfb2e2416127a6f6b156731873393746b9e7b/http%3A//botaday.com\">botaday.com</a>"
}