how do I remove mandiant cyber security ransomware from a mac pro

Mac Pro hase for browsers Safari and Fire Fox. A website infected the mac with the Madriant Ransomware virus via the Firefox browser. It locked up the mac, gave the usually banner message associated with that virus. Turned off the mac for about 15 -30 secs, turned it on, logged back in and cleared all Firefox browser collected information. I do not see any evidence of this virus but it is probably still residing on the system. What is the procedures to manually clean this virus off a Mac Pro. I am an expert in Windows type machines but don't know much about Mac OS intricacies. Mac OS is OS X, Mountain Lion.

Thanks in advance.

Gary