Examine source code of whenIInstaledFirefox

{
  "theme": {
    "images": {
      "theme_frame": "header.png"
    },
    "colors": {
      "frame": "#2e0000",
      "tab_background_text": "#ffffff"
    }
  },
  "version": "2.0",
  "name": "whenIInstaledFirefox",
  "manifest_version": 2,
  "description": "It's typical theme which I make for me."
}