Examine source code of cdnExtension

{
  "manifest_version": 2,
  "name": "Beastify",
  "version": "1.0",
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "borderify.js"
      ]
    }
  ],
  "description": "Adds a browser action icon to the toolbar. Click the button to choose a beast. The active tab's body content is then replaced with a picture of the chosen beast. See https://developer.mozilla.org/en-US/Add-ons/WebExtensions/Examples#beastify",
  "homepage_url": "https://github.com/mdn/webextensions-examples/tree/master/beastify",
  "icons": {
    "48": "icon.png"
  },
  "permissions": [
    "activeTab"
  ],
  "browser_action": {
    "default_icon": "icon.png",
    "default_title": "Beastify",
    "default_popup": "beast.html"
  },
  "web_accessible_resources": [],
  "browser_specific_settings": {
    "gecko": {
      "id": "{a53461c2-511e-4792-b868-3bfcaaa09060}"
    }
  }
}