Examine source code of Fx Preview Dark

{
  "manifest_version": 2,
  "version": "5.0",
  "name": "Fx Preview Dark",
  "theme": {
    "images": {},
    "properties": {},
    "colors": {
      "toolbar": "rgb(20, 19, 23)",
      "bookmark_text": "rgb(255, 255, 255)",
      "frame": "rgb(0, 0, 0)",
      "tab_background_text": "rgb(255, 255, 255)",
      "toolbar_field": "rgb(20, 19, 23)",
      "toolbar_field_text": "rgb(255, 255, 255)",
      "tab_line": "rgb(56, 34, 100)",
      "popup": "rgb(56, 34, 100)",
      "popup_text": "rgb(255, 255, 255)",
      "tab_loading": "rgb(255, 255, 255)",
      "popup_highlight_text": "rgb(255, 255, 255)",
      "popup_highlight": "rgb(56, 34, 100)",
      "toolbar_field_border": "rgb(56, 34, 100)",
      "toolbar_field_border_focus": "rgb(56, 34, 100)",
      "toolbar_field_focus": "rgb(20, 19, 23)",
      "ntp_background": "rgb(20, 19, 23)",
      "ntp_text": "rgb(255, 255, 255)"
    }
  }
}