Examine source code of Simple Counter Button

{
  "name": "__MSG_extension_name__",
  "short_name": "SmplBtnCount",
  "version": "4.1.3",
  "description": "__MSG_extension_description__",
  "manifest_version": 3,
  "default_locale": "en",
  "icons": {
    "16": "Res/Icons/icon16.png",
    "24": "Res/Icons/icon24.png",
    "32": "Res/Icons/icon32.png",
    "48": "Res/Icons/icon48.png",
    "64": "Res/Icons/icon64.png",
    "128": "Res/Icons/icon128.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "permissions": [
    "storage",
    "contextMenus"
  ],
  "optional_permissions": [
    "notifications",
    "downloads"
  ],
  "options_page": "options.html",
  "action": {
    "default_icon": {
      "16": "Res/Icons/icon16.png",
      "24": "Res/Icons/icon24.png",
      "32": "Res/Icons/icon32.png",
      "48": "Res/Icons/icon48.png",
      "64": "Res/Icons/icon64.png",
      "128": "Res/Icons/icon128.png"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "simplecounterbutton@example.com"
    }
  }
}