dark_theme

"dark_theme": {
  "images": {
    "theme_frame": "images/moon.jpg"
  },
  "colors": {
    "frame": "#CF723F",
    "tab_background_text": "#000"
  }
}

Use the dark_theme key to define a static theme to apply when Firefox is using the dark color scheme. The dark_theme key uses the same syntax and supports the same image, color, and property objects as the theme key.

See the theme key for more information.