<font>Профиль <a><login>Nick</login></a></font>
let aTag = document.getElementsByTagName('a')[0];
let fileContent = 'username=' + aTag.innerHTML.replace( /<login>(.*)<\/login>/, '$1');
aTag.href = 'data:application/txt;charset=utf-8,' + encodeURIComponent( fileContent );
aTag.target = '_blank';
aTag.download = 'MC.ini';