I've installed Mozilla Firefox, same problem, with a new clean Windows. Just after starting the browser (Internet Explorer on new Windows XP), i had exactly the same CPU problem. I reinstalled Windows and let D and E as they were. I had 3 partitions on that computer C,D and E. I've tried MalwareBytes, SpyBot Search and Destroy, Avira, Avast, Nod32, Pc Utilities and many other programs (anti spy, antivirus, anti malware, etc.), nothing, but nothing worked. The computer worked fine, maybe a little slow, but when i opened any sort of page with any browser the cpu was going up to 100% and was making my computer to run very slow.
I actually had the same problem with one of my computers.