From the Firefox website:
Anti-MalwareFirefox 3 protects you from viruses, worms, trojan horses and spyware. If you accidentally access an attack site, you’ll receive a full-sized browser message as a warning. A continuously updated list of attack-sites tells us when to stop you from browsing, so there’s nothing for you to update or maintain.
Anti-Virus SoftwareFirefox 3 integrates elegantly with your antivirus software. When you download a file, your computer’s antivirus program automatically checks it to protect you against viruses and other malware, which could otherwise attack your computer. [available in Windows only]
Anti-PhishingShop and do business safely on the Internet. Firefox gets a fresh update of web forgery sites 48 times in a day, so if you try to visit a fraudulent site that’s pretending to be a site you trust (like your bank), a browser message—big as life—will stop you.
(And not long ago, I had a phishing incident vis–à–vis my bank.)
Download Firefox here. (It's free!)