I hope many will respond to this question as it is a matter of opinion to some extent at least.
I read that Firefox offers far better protection against viruses and worms (and hackers?). And I gather that MSIE is very vulnerable to security flaws BECAUSE it's been around for years and so its limitations have been probed and discovered (and virus programs written to exploit the weaknesses.)
Is the primary reason then why Firefox appears highly rated for its security efficiency because it hasn't been around for years and not because it's done a super++ job of keeping viruses out? And I keep up to date with virus updates (NAV) and all of Microsoft's Windows updates that are classified as 'critical' I also runSpybot at least every 2 months.
I've used MSIE since September 98, along with NAV, firewalls and recently a router. The only virus to ever hit me was the Chernobyl virus and that was only because I had not installed virus software at that time. And for a long time I had dial-up; I did not get broadband until July or August 2002.