Examine source code of Earth Carbon

{
  "theme": {
    "images": {
      "theme_frame": "thunderbird-carbon-earth.jpg"
    },
    "colors": {
      "frame": "#b0a7a7",
      "tab_background_text": "#d9d2d2"
    }
  },
  "version": "2.0",
  "name": "Earth Carbon",
  "manifest_version": 2,
  "description": "Earth Carbon"
}