I went to »
test-ipv6.com just to see what it would say, and it said that I had "Broken DNS AAAA Lookups".
In the possible causes, it listed the OS, the DNS server, and Firefox. They said to go to about:config in Firefox and check "network.dns.disableIPv6". So I checked, and it's set to true.
So, other than IPv6 isn't fully implemented yet, is there any reason why only Firefox disables IPv6 lookups?