Comment 52 for bug 308181

resolve() can stay to resolve cname and A records (and backwards compat)
a method probably called resolveWithType(...) could implement all other extensions.

Probably we need to extend nsIDnsRecord to hold key/value data (propertybag) of the different RR types (for example weight, priority, type, ip, hostname) or have them as a bunch of typed members.
You can see what kind of members we need looking at the DNS RR types here http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dns/dns/dns_structures.asp