This question has probably been asked many times before as well, but here we go:
There aren't many Viruses, make it easy, there aren't any serious ones. Think this way: what damage can a Virus do if you aren't logged in as root? It could only delete temp. files or personal files, but the system cannot be touched.
As for the firewall - i don't know what firewall you're using...neither do I know many.
Hope this helps