Firefox can't establish connection to the server

Hi, ALL,
Today my father's computer hit very interesting issue.
Running latest FF I got the subj.

Everything else works. IE works (in fact I'm writing this from IE - version 8.0). Skype works - it is connected and online. I can ping without any data loss.

I'm running Windows XP SP 3 32-bit with ZoneAlarm and Avira AV (both updated).
Trying to kill FF from ZoneAlarm or change the access there does not help.

Its only FF.

Googling gives couple of old thread stating that the problem came in with FF 3 and went away with FF 6.

The problem just started. My dad is a happy FF user and he never got any issue with it.

Any hints?

Thank you.

P.S.: I thinkl that this thread does not belong in Malware forum, but I don't know where to put it. Any help in this matter will be appreciated as well.