Examine source code of Battery Status

{
  "manifest_version": 2,
  "name": "Battery Status",
  "description": "See the battery status on the toolbar.  Only compatible with Windows... yet.  If you like the addon, please consider to support with a Ko-fi.",
  "version": "1.1.1",
  "icons": {
    "32": "icons/32/8.png",
    "48": "icons/48/8.png",
    "64": "icons/64/8.png",
    "128": "icons/128/8.png"
  },
  "browser_action": {
    "default_icon": "icons/32/8.png",
    "default_title": "Battery Status",
    "default_popup": "settings/index.html"
  },
  "options_ui": {
    "page": "options_ui/index.html",
    "open_in_tab": false
  },
  "background": {
    "scripts": [
      "script/index.js"
    ],
    "persistent": true
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{12cc0bd0-af8c-445b-bdf9-77bab80b332f}"
    }
  },
  "permissions": [
    "storage",
    "tabs",
    "http://localhost:3300/*"
  ]
}