Speaking of caching, are browsers already doing all the caching that is practical on modern machines? I vaguely remember years ago downloading a special program

Speaking of caching, are browsers already doing all the caching that is practical on modern machines? I vaguely remember years ago downloading a special program that sped up the internet by performing more aggressive caching than the browser was capable of (basically it was just a caching proxy). Everything was noticeably quicker. Though these days things probably feel slower because every website is loaded down with 3rd party JS from 100 different sites...