Examine source code of Firefox 4 Background

{
  "theme": {
    "images": {
      "theme_frame": "ff4blue_header.png"
    },
    "colors": {
      "frame": "rgba(229,230,232,1)",
      "tab_background_text": "#000"
    }
  },
  "version": "2.0",
  "name": "Firefox 4 Background",
  "manifest_version": 2,
  "description": "It's the background color from Firefox 4, created to make the background of the Menu and Navigation toolbars the same soft blue as the Bookmark and Tab toolbars."
}