Clone of Firefox Bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1870497

> User Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:120.0) Gecko/20100101 Firefox/120.0
> 
> Steps to reproduce:
> 
> Set up the following DNS records:
> 
> www1.test A 192.0.2.1
> _www2.test A 192.0.2.1
> www3._www3.test A 192.0.2.1
> www_4.test A 192.0.2.1
> -www5.test A 192.0.2.1
> www6.-www6.test A 192.0.2.1
> 
> cname1.test CNAME www1.test
> cname2.test CNAME _www2.test
> cname3.test CNAME www3._www3.test
> cname4.test CNAME www_4.test
> cname5.test CNAME -www5.test
> cname6.test CNAME www6.-www6.test
> 
> Open all of the "cname1" to "cname6" hostnames as URLs in Firefox.
> 
> Actual results:
> 
> The "cname5" hostname returns "Server Not Found".
> 
> The other names can be resolved and Firefox will connect to them.
> 
> Expected results:
> 
> All of "cname1" to "cname6" can be resolved and Firefox will connect to them.
> 
> The hostnames used in CNAME targets (or chains of CNAME targets) should not be subject to the same validation as the hostname in the URL.

In Firefox on Linux we use glibc getaddrinfo to resolve hostnames. I think fixing this in glibc would be best.