Examine source code of Velja

{
  "manifest_version": 3,
  "name": "Velja",
  "version": "1.2.3",
  "description": "Open a link or the current website in another browser using Velja (macOS only).",
  "homepage_url": "https://sindresorhus.com/velja",
  "browser_specific_settings": {
    "gecko": {
      "id": "{7599bb55-1e8e-445a-9e32-66da6e1d6749}",
      "strict_min_version": "123.0"
    }
  },
  "icons": {
    "48": "images/icon-48.png",
    "96": "images/icon-96.png",
    "128": "images/icon-128.png",
    "256": "images/icon-256.png",
    "512": "images/icon-512.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ],
    "type": "module"
  },
  "action": {
    "default_title": "Open in Velja",
    "default_icon": {
      "16": "images/toolbar-icon-16.png",
      "19": "images/toolbar-icon-19.png",
      "32": "images/toolbar-icon-32.png",
      "38": "images/toolbar-icon-38.png",
      "48": "images/toolbar-icon-48.png",
      "72": "images/toolbar-icon-72.png"
    }
  },
  "permissions": [
    "activeTab",
    "contextMenus"
  ]
}