i want online security. so that viruses and malware should not enter my PC
See, this a more to-the-point question.
For this no browser is enough.
But, I would recommend these things:-
FF + Addons (PhishTank, NoScript, AdBlockPlus, JSView, WOT)
+
A good Internet Security Solution:-
Paid: KIS2009 (2010 is also out I've heard)+Adware
Free: Avira Free version (antivirus only)/AVG8 + Komodo + Adware +Malwarebytes Malware remover
These would be pretty much resource hog...so, if u don't have enough (at least 2GB) RAM, don't install all.