Imagine

[Thomas Schäfer]

there is an ipv6-only net. All base services like smtp(s), imap(s), ntp, 
printing, ssh,  dns-resolver... and so on are ipv6 capable.
What is to do with the "old" world - specifically http(s)/ftp-services?
Ok - a proxy is good answer. But now my actual question:

Is there a possibillity to make simple proxysettings in Firefox in this way:
site has only A-Record-- > use proxy
site has AAAA-Record--> connect directly

Is this possible with a Proxy Auto-Config (pac) -file?

Regards,

Thomas