Examine source code of Add to Calendar

{
  "manifest_version": 2,
  "name": "Add to Calendar",
  "version": "1.1",
  "description": "Add selected date/time text to your favorite calendar.",
  "minimum_firefox_version": "79.0",
  "browser_specific_settings": {
    "gecko": {
      "id": "{1b67ec5a-1615-41b1-a359-3c1d45a823b4}"
    }
  },
  "permissions": [
    "contextMenus",
    "downloads",
    "tabs"
  ],
  "background": {
    "scripts": [
      "background.js",
      "ics.js"
    ]
  },
  "icons": {
    "48": "icons/calendar.png",
    "256": "icons/calendar-logo.png"
  }
}