They use Fira Sans and Fira Mono in a bunch of different weights.<p>Looking at the source for &lt;<a href="http:&#x2F;&#x2F;www.gnu.org&#x2F;software&#x2F;emacs&#x2F;fira.css&gt;" rel="nofollow">http:&#x2F;&#x2F;www.gnu.org&#x2F;software&#x2F;emacs&#x2F;fira.css&gt;</a>, I can&#x27;t help but wonder if mobile^W OS vendors could make the Web faster for their users if they&#x27;d just bundle every single popular free (beer and&#x2F;or speech) font with their OSs and keep the fonts up-to-date.<p>Of course, you should be sending along far-future Expires and Cache-Control headers, but this&#x27;ll still be slower than local() accessing fonts that&#x27;re bundled with the OS when someone visits a new site.