Examine source code of Ultra Dark Mode

{
  "manifest_version": 2,
  "name": "Ultra Dark Mode",
  "version": "1.2.1",
  "author": "Harry Ng",
  "description": "__MSG_extension_description__",
  "default_locale": "en",
  "browser_action": {
    "default_title": "Ultra Dark Mode",
    "default_icon": {
      "19": "icons/dm_active_19.png",
      "38": "icons/dm_active_38.png"
    },
    "default_popup": "ui/popup/index.html"
  },
  "icons": {
    "16": "icons/dm_16.png",
    "48": "icons/dm_48.png",
    "128": "icons/dm_128.png"
  },
  "background": {
    "page": "background/index.html"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "inject/fallback.js"
      ],
      "run_at": "document_start",
      "all_frames": true,
      "match_about_blank": true,
      "world": "MAIN"
    },
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "inject/index.js"
      ],
      "run_at": "document_start",
      "all_frames": true,
      "match_about_blank": true,
      "world": "ISOLATED"
    }
  ],
  "permissions": [
    "alarms",
    "contextMenus",
    "storage",
    "tabs",
    "theme",
    "<all_urls>"
  ],
  "optional_permissions": [],
  "commands": {
    "toggle": {
      "suggested_key": {
        "default": "Alt+Shift+D"
      },
      "description": "__MSG_toggle_extension__"
    },
    "addSite": {
      "suggested_key": {
        "default": "Alt+Shift+A"
      },
      "description": "__MSG_toggle_current_site__"
    },
    "switchEngine": {
      "description": "__MSG_theme_generation_mode__"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "darkmode@darkmodes.org",
      "strict_min_version": "128.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    },
    "gecko_android": {
      "strict_min_version": "128.0"
    }
  }
}