internet explorer and firefox are the most widely used browsers.these hence r easy targets for hackers to harm millions of pcs.here's what i do,i use lesser used browsers like opera or arora.
I hav kaspersky internet security and it has a safe run folder.add your browser to that list.Now watevr u browse,and watevr it downloads or indirectly changes registry or system setting all get reverted back like b4 once u close the browser.the only letdown is that your saved browser history etc also is removed.this is a perfect way to avoid viruses or malware gettin inside ur system by your browser