Examine source code of TenderIn

{
  "manifest_version": 2,
  "name": "Tenderin browser extension",
  "version": "1.0.5",
  "description": "Adds a button to a specific website",
  "permissions": [
    "activeTab",
    "storage",
    "http://*/*",
    "https://*/*"
  ],
  "content_scripts": [
    {
      "matches": [
        "https://www.tenderned.nl/*"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_idle"
    }
  ],
  "icons": {
    "16": "icon.png",
    "48": "icon.png",
    "128": "icon.png"
  },
  "browser_action": {
    "default_title": "Tenderin browser extension"
  },
  "web_accessible_resources": [
    "logo.png",
    "download.svg",
    "login.svg"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{38b1bffa-a9c6-4a76-ba05-1e1da0b8406b}"
    }
  }
}