How to use the browser's (chrome/firefox) HTML/CSS/JS rendering engine to produce PDF?

I'm not an expert but PhamtomJS seems to be the right tool for the job. I'm not sure though about what headless browser it uses underneath (I guess it is chrome/chromium)

var page = require('webpage').create();page.open('http://github.com/', function() {     var s = page.evaluate(function() {         var body = document.body,             html = document.documentElement;        var height = Math.max( body.scrollHeight, body.offsetHeight,             html.clientHeight, html.scrollHeight, html.offsetHeight );        var width = Math.max( body.scrollWidth, body.offsetWidth,             html.clientWidth, html.scrollWidth, html.offsetWidth );        return {width: width, height: height}    });    console.log(JSON.stringify(s));    // so it fit ins a single page    page.paperSize = {        width: "1980px",        height: s.height + "px",        margin: {            top: '50px',            left: '20px'        }    };    page.render('github.pdf');    phantom.exit();});

Hope it helps.

Firefox has an API method for that: https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/tabs/saveAsPDF

browser.tabs.saveAsPDF({})  .then((status) => {    console.log('PDF file status: ' + status);  });

However, it seems to be available only for Browser Extensions, not to be invoked from a web page.

I'm still looking for a public API for that...