To make the images load faster, we should add a resource hint, making the browser preconnect to upload.wikimedia.org. Preconnect in this case means the browser will do DNS+TCP+TLS as soon as it cann for that domain and hopefully a little earlier than today.
To do that, we need to add:
<link rel="preconnect" href="//upload.wikimedia.org ">
Here's an example of how it looks today.
{F3224213, width=500}
Preconnect is supported by Chrome, Firefox and Opera on Desktop and Chrome & Android Browser on Android (http://caniuse.com/#feat=link-rel-preconnect).
Quick draft to show the syntax of `preconnect`: <https://gerrit.wikimedia.org/r/#/c/348807/4/includes/OutputPage.php>
Potential gotcha from @Krinkle at <https://gerrit.wikimedia.org/r/#/c/348807/>:
> MediaWiki ParserOutput doesn't currently track the effective image url(s). Only the file names. Extracting the host from File::getPath() manually is tricky because file path to original file and thumbnail may differ. E.g. when using a foreign repository like Wikimedia Commons, some configurations host thumbnails in the local file backend (instead of "hot linking").