Is it possible to control Firefox's DNS requests in an addon?

Question

I was wondering if it was possible to intercept and control/redirect DNS requests made by Firefox?
The intention is to set an independent DNS server in Firefox (not the system's DNS server)

Answer 1

No, not really. The DNS resolver is made available via the nsIDNSService interface. That interface is not fully scriptable, so you cannot just replace the built-in implementation with your own Javascript implementation.

But could you perhaps just override the DNS server?

The built-in implementation goes from nsDNSService to nsHostResolver to PR_GetAddrByName (nspr) and ends up in getaddrinfo/gethostbyname. And that uses whatever the the system (or the library implementing it) has configured.

Any other alternatives?

Not really. You could install a proxy and let it resolve domain names (requires some kind of proxy server of course). But that is a very much a hack and nothing I'd recommend (and what if the user already has a real, non-resolving proxy configured; would need to handle that as well).