setExtraHTTPHeaders(headers)

import { chromium } from 'k6/experimental/browser';

export default async function () {
  const browser = chromium.launch();
  const page = browser.newPage();
  
  page.setExtraHTTPHeaders({ 'foo': 'bar' });
  const url = await page.goto('https://test.k6.io/browser.php');

  console.log(url.request().headers().foo) // prints bar
}