Worried about malware in Firefox

I just got a bit worried, when I used Google in Firefox. I have been using windows for many years with antivirus on this net coection, and I have never before encountered the message: “Our systems have detected unusual traffic from your computer network." Now after a couple of month on Ubuntu, I received this message. There has been another tread :http://ubuntuforums.org/showthread.php?t=2280206. Her the cause where malware in Chrome, but there where no description of how this was removed. What malware detector do you recommend, and what program should I use to monitor my net coection?

I have a rather fresh installed Ubuntu 14.04 LTS and only a limited number of programs is installed.

Best regards
ZF