An alternative is the Team Cymru MHR 1.1
Firefox extension. The purpose of the extension is to check downloaded files against multiple anti-virus and anti-malware products from the Firefox download window. All you need do is click "Check MHR" shown under the time in the download window:
Note: Neither this nor the VTzilla extension replace your antivirus software. Rather, consider the extension a supplement. With the Team Cymru MHR Firefox extension, in the event the download is identified as malware, it can be deleted rather than installed.