Examine source code of Threes Company

{
  "theme": {
    "images": {
      "theme_frame": "threesheader.jpg"
    },
    "colors": {
      "frame": "#ffffff",
      "tab_background_text": "#000000"
    }
  },
  "version": "2.0",
  "name": "Threes Company",
  "manifest_version": 2,
  "description": "The first and only Three's Company skin for your FireFox created by me.  Hope you'll check out my web site as well!"
}