strange redirection

I entered www.alibris.com in Netscape’s address windowlet and landed in a search engine with an unrememberable url. After a couple of clicks this heroic – self-sytled – search engine got me to alibris, but I would have preferred to get there directly. I tried with a few other urls, but only alibris got me the heroic search engine. I closed Netscape and tried on IE, where everything went fine. Then I restarted Netscape and the problem was gone. What kind of virus or spyware might this have been? I have Norton antivirus and Windows firewall.