In head.html we have:

<script src="{{ "/assets/js/vendor/modernizr-2.8.3-respond-1.4.2.min.js" | relative_url }}"></script>

which I suspect is no longer necessary. Modernizr is a JS library to feature detect new CSS features and allow you to work around their absence. Respond.js is a polyfill for CSS media queries. These were necessary when the site was first designed a decade ago, but I suspect all the CSS features we're using have wide browser support now. You can see the exact features we're querying in the "build" comment at the top of the vendor JS file. There many of them, but also many we're not using (indexeddb, websockets, etc.). I think we could safely remove this script tag and also the vendor JS file, but that'd need thorough testing.