"imgs.xkcd.com uses an invalid security certificate"
The HTTP Everywhere 4.0development.15 ruleset for xkcd rewrites this URL:
However, in regards to the cert for imgs.xkcd.com, Firefox 27.0.1 on Mac 10.9.2 reports, "The certificate is only valid for the following names: *.voxcdn.com , voxcdn.com".
So, attempting to load the image in Firefox results in a broken image, as Firefox refuses to load the image, with the error "ssl_error_bad_cert_domain".
What happens: broken image What should happen: image should be displayed properly
This bug is particularly ironic because the page at https://www.eff.org/https-everywhere has this link:
[a href="https://www.xkcd.com/208"]clever technology[/a]
which triggers the broken image on that xkcd page.