originally filed by @gravityrail

PageSpeed detected opportunities to improve load speed by preloading fonts.

In this particular case, adding the following to a test plugin improved scores.

add_action( 'wp_head', function() {
echo '<link rel="preload" href="https://boosttest.mystagingwebsite.com/wp-content/themes/uncode/library/fonts/uncode-icons.woff2" as="font" type="font/woff2" crossorigin/>';
}, -PHP_INT_MAX );

We can/should use the Lighthouse results themselves to "discover" which fonts can/should be preloaded on a given URL. Note the type and crossorigin attributes are required if the font is served from a CDN.

Separately we may want to modify CSS to serve fonts from the origin. Browsers now typically segment caches by origin anyway so there's no caching benefit to having a shared instance, and incurring the DNS cost may cancel out any CDN benefits.

Some initial exploration notes in the old repo in a comment here: 664-gh-Automattic/jetpack-boost