I have "auto-detect proxy settings" enabled which is essentially the same thing and can confirm that Firefox is making DNS requests even though HTTP is directed through the proxy (configured from wpad.dat, proxy.pad).
If I use fixed proxy settings (ip:port) in firefox and disable wpad.dat/proxy.pac completely firefox stops makeing DNS requests.
I have "auto-detect proxy settings" enabled which is essentially the same thing and can confirm that Firefox is making DNS requests even though HTTP is directed through the proxy (configured from wpad.dat, proxy.pad).
If I use fixed proxy settings (ip:port) in firefox and disable wpad.dat/proxy.pac completely firefox stops makeing DNS requests.
Tested on V 3.0.10 Windohz Vista.