In an SDK-based add-on I need to handle resources that are not publicly available differently.
for file: and resource: etc. URLs its rather obvious that they are, for https?: It would be a very good approximation to know the host-ip of those resources.
I have one more question: does record.getNextAddrAsString() always return IP adresses, or do I have to call resolve() recursively on the result unitl it is an IP address?
No idea, easiest way to find out is to see what you get when you query something defined with a CNAME pointing somewhere else. I would assume it always returns an IP, especially looking at the IDL definition of nsIDNSRecord.