Examine source code of Firefox and Icefox.

{
  "theme": {
    "images": {
      "theme_frame": "header.png"
    },
    "colors": {
      "frame": "rgba(229,230,232,1)",
      "tab_background_text": "#1b2d5c"
    }
  },
  "version": "2.0",
  "name": "Firefox and Icefox.",
  "manifest_version": 2,
  "description": "Two cute little foxes looking rather confused at each others' existence. \n\n\"Why are you floating?\" said Ice.\n\n\"Why are you blue?!?\" replied Fire.\n\nThis theme may not fit your custom toolbar layouts... but that's ok."
}