&gt; The problem is that almost everyone hosts their own version of jQuery.<p>Any site that expects users to trust it with sensitive data should not be pulling in any off-site JavaScript.<p>As for checksumming, browser vendors don&#x27;t need to pre-load popular JavaScript libraries (though they might choose to do so, especially if they already ship those libraries for use by their extensions and UI).  But checksum-based caching means the cost still only gets paid by the first site, after which the browser has the file cached no matter who references it.