Examine source code of Open Multiple URLs

{
  "manifest_version": 2,
  "name": "Multi URL Opener",
  "version": "1.0",
  "description": "Open multiple URLs with a single button click.",
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": {
      "16": "icons/icon16.png",
      "48": "icons/icon48.png",
      "128": "icons/icon128.png"
    }
  },
  "icons": {
    "16": "icons/icon16.png",
    "48": "icons/icon48.png",
    "128": "icons/icon128.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "yourextensionid@example.com"
    }
  },
  "permissions": [
    "tabs"
  ]
}