I am having trouble with a redirect virus; how to fix?

I think I have a virus or spyware on my computer. It redirects me to a third-party site (something like LinkBucks) when I try to visit Facebook, Google or YouTube. This happens in both Safari and in Mozilla Firefox. I have tried scanning with ClamX, MacScan, but they are not finding any viruses. I also downloaded a kit that scans the computer for DNS redirect changer viruses, but it can't find any. What should I do now?