Examine source code of Print Watermark

{
  "manifest_version": 3,
  "name": "Print Watermark",
  "version": "1.0",
  "description": "Add diagonal watermark to pages before printing",
  "permissions": [
    "activeTab",
    "storage",
    "scripting"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "printwatermark@extension",
      "strict_min_version": "142.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "action": {
    "default_popup": "popup.html",
    "default_icon": {
      "16": "16.png",
      "48": "48.png",
      "128": "icon.png"
    }
  },
  "icons": {
    "16": "16.png",
    "48": "48.png",
    "128": "icon.png"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ]
    }
  ]
}