Visiting https://signed.bad.horse in Nightly, it shows the following text, missing the current date.
signed.bad.horse has a security policy called HTTP Strict Transport Security (HSTS), which means that Nightly can only connect to it securely. You can’t add an exception to visit this site.
Your computer clock is set to . Make sure your computer is set to the correct date, time, and time zone in your system settings, and then refresh signed.bad.horse.
If your clock is already set to the right time, the website is likely misconfigured, and there is nothing you can do to resolve the issue. You can notify the website’s administrator about the problem.
It seems to be because the substitution only happens on one element matching the
wrongSystemTime_systemDate2 id, while there are 4. Putting the
es_nssBadCert_SEC_ERROR_EXPIRED_ISSUER_CERTIFICATE div before
es_nssBadCert_SEC_ERROR_EXPIRED_CERTIFICATE makes this case work, but of course that doesn't help in general.