I was struggling about 2 hours to fix a firefox dns problem!
He could not resolve addresses - dns problem.
But there was no problem with ips.
I could browse with opera , konqueror but not firefox.
2-3 hours for a so simple problem can drive a developer NUTS!
And I google and google until....
Someone mentioned /etc/hosts and it struck me - I had changed it.

And then opened it and saw all these lines that I kept pasting and screwed the hosts file. Corrected them and firefox came back.

But on the other hand firefox... The "blessed" child of open source ...
The hope to get away from IE .. The program that WE recommend on the footer of this page...
If he finds a screwed hosts file then ......... no DNS at all.
How nice of yours Mr Firefox!