Examine source code of Silent Label Printer Pro

{
  "manifest_version": 2,
  "name": "Silent Label Printer Pro",
  "version": "1.0.0",
  "description": "Silent printing for all label printers via QZ Tray",
  "permissions": [
    "storage",
    "activeTab",
    "https://gramguardian.com/*",
    "https://*.gramguardian.com/*"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "https://gramguardian.com/*",
        "https://*.gramguardian.com/*"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_start"
    }
  ],
  "web_accessible_resources": [
    "injected.js"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "silent-printer@gramguardian.com",
      "strict_min_version": "140.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  }
}