Examine source code of Themeinator

{
  "manifest_version": 3,
  "name": "Themeinator",
  "version": "1.0.2",
  "description": "A customizable Firefox theme that automatically adapts your system's light/dark mode",
  "permissions": [
    "theme",
    "storage",
    "browserSettings",
    "search"
  ],
  "host_permissions": [
    "<all_urls>"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{0975c637-1a5b-4a3b-a79e-b7f5817e9494}",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "developer": {
    "name": "Coding Otaku",
    "url": "https://codingotaku.com"
  },
  "homepage_url": "https://codingotaku.com/users/otaku/projects/themeinator",
  "background": {
    "scripts": [
      "js/background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "js/system-theme-notifier.js"
      ]
    }
  ],
  "action": {
    "default_popup": "popup.html",
    "default_icon": {
      "16": "icons/icon-16.png",
      "32": "icons/icon-32.png",
      "48": "icons/icon-48.png"
    },
    "default_title": "Themeinator"
  },
  "options_ui": {
    "page": "options.html"
  },
  "chrome_url_overrides": {
    "newtab": "newtab.html"
  },
  "icons": {
    "16": "icons/icon-16.png",
    "32": "icons/icon-32.png",
    "48": "icons/icon-48.png",
    "96": "icons/icon-96.png"
  }
}