Examine source code of Firefox Grayscale Tiled

{
  "theme": {
    "images": {
      "theme_frame": "header_ffl_grayTiledSemitransp.jpg"
    },
    "colors": {
      "frame": "#000000",
      "tab_background_text": "#000000"
    }
  },
  "version": "2.0",
  "name": "Firefox Grayscale Tiled",
  "manifest_version": 2,
  "description": "The Firefox logo in grayscale--tiled and semitransparent"
}