Here's a bookmarklet that does the same thing:

    javascript:(()=>{d=new Date(1171843200000+Math.random()*(Date.now()-1171843200000));window.location.href=`https://news.ycombinator.com/front?day=${d.getFullYear()}-${('0'+(d.getMonth()+1)).slice(-2)}-${('0'+d.getDay()).slice(-2)}`;})()