Examine source code of Save tab PDF

{
  "manifest_version": 2,
  "name": "Save tab PDF",
  "version": "1.1",
  "description": "Adds a button to save the current page as a PDF",
  "icons": {
    "48": "icons/icon48.png",
    "128": "icons/icon128.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{39c1b03a-0a2e-4fdb-a34e-791d610ee8dc}",
      "strict_min_version": "78.0"
    }
  },
  "permissions": [
    "tabs",
    "activeTab"
  ],
  "browser_action": {
    "default_icon": "icons/icon48.png",
    "default_title": "Save page as PDF"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  }
}