Examine source code of Cut Dark Fx

{
  "theme": {
    "images": {
      "theme_frame": "Firefox-Cut-Dark-Header.png"
    },
    "colors": {
      "frame": "rgba(229,230,232,1)",
      "tab_background_text": "#ffffff"
    }
  },
  "version": "2.0",
  "name": "Cut Dark Fx",
  "manifest_version": 2,
  "description": "Reveal more of your Personas.\nAdd this to your userChrome.css.\n.searchbar-textbox  {\nopacity: 0.4 !important;\n}\n.searchbar-textbox[focused=\"true\"]{\nopacity: 0.8 !important;\n}\n#urlbar {\nopacity: 0.4 !important;\n}\n#urlbar[focused=\"true\"]{\nopacity: 0.8 !important;\n}"
}