It loads fine for me. Looks like this https://imgur.com/a/lrTMBmE
--2019-01-18 13:46:40-- http://acid3.acidtests.org/support-a.png
Resolving acid3.acidtests.org (acid3.acidtests.org)... 75.119.197.251
Connecting to acid3.acidtests.org (acid3.acidtests.org)|75.119.197.251|:80... connected.
HTTP request sent, awaiting response... 404 Not Found
2019-01-18 13:46:40 ERROR 404: Not Found.
It's actually sending a PNG file, but with a 404 response.