Examine source code of the new firefox...

{
  "theme": {
    "images": {
      "theme_frame": "headernewfirefox.jpg"
    },
    "colors": {
      "frame": "rgba(229,230,232,1)",
      "tab_background_text": "#000"
    }
  },
  "version": "2.0",
  "name": "the new firefox...",
  "manifest_version": 2,
  "description": "the new Firefox logo (a sketch of it, anyways) overlayed on an abstract background"
}