Antivirus and firewall software for linux.

No need to ponder whether you need a firewall for linux or not. It's a done deal. You definitely do.
If the creators of the software thought you didn't need one, why would they go to the lengths they have in providing one as default, at least in the distributions I've tried. With Ubuntu Gutsy Gibbon and OpenSuse it's there when you log on to the internet, though don't wast your time looking for icons on the toolbar, there aren't any.
You can prove it for yourself by going to the Shields Up website and have them test it for you. Look for the all green results and you know you're safe. Alternatively, there is the very useful Auditmypc website which does the same test, plus it has an anonymous and popup tests as well.
Opinion is mixed about the question of antvirus software, with the majority saying no, you don't need it. Some users even wonder why you're asking the question at all.
Fact is that ClamAV, which is one of the well known linux antivirus applications, exists at all proves that viruses do exist in linux. I can honestly say, after over a year of using only the linux operating system on the internet, I don't have any concerns about computer viruses on my pc. Linux has given me that confidence.
If in doubt, install ClamAV and run it periodically. You can do that just for peace of mind. Me, I did this at first, now I don't bother at all. I don't feel the need to have it at all on my computer.