Need Help Please: What got into my computer?

Yesterday I went to a reputable website and got a redirect to what looked like a Google web page showing the results of a search. The search was for the web site I intended to visit but with a prefix in the "Google" search box: "415++++ call the governor" . The same thing happened for the next website I visited. I did actually click on one of the results and it brought me to an article of that name ("Call the Governor") on the original website I had intended to visit initially. I closed and reopened my browser (Firefox 5) and the redirects did not occur anymore.

I use NIS 2011 on access full time. I then scanned with both Hitman Pro and Malwarebytes and they found nothing.

Today I started a free trial of Malwarebytes Pro real time with NIS 2011. All day, maybe once an hour I get a pop-up from Malwarebytes saying: "Blocked an attempt by your computer to access a malicious website: xxx.xxx.xxx.xxx. And specified port 60305.

I searched the numbered url ( was of those like 212.575.175.384 - these are just random numbers I am using). The site is hosted in Luxenburg and according to ThreatExpert report it "Produces outbound traffic. Downloads/requests other files from Internet. Creates a startup registry entry.  http://www.threatexpert.com/report.aspx?md5=3938169979a8d5278971650033207ca2

My Norton history shows nothing.

What has infected my PC and do I have any good alternative to reformatting or continuing to rely on Malwarebytes Pro to block it.