Examine source code of html-360-viewer

{
  "description": "Adds browser action icon to toolbar to open packaged web page. See https://developer.mozilla.org/en-US/Add-ons/WebExtensions/Examples#open-my-page-button",
  "manifest_version": 2,
  "name": "open-my-page",
  "version": "1.0",
  "homepage_url": "https://github.com/mdn/webextensions-examples/tree/master/open-my-page-button",
  "icons": {
    "48": "icons/page-48.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_icon": "icons/page-32.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{14099db9-589e-43d0-b793-5243b87f979c}"
    }
  }
}