Very useful security addon for downloads; has some limitations Rated 4 out of 5 stars
Very useful for pre-screening downloads. Initially it just gives you information based on the site. But if you're sending the actual download file URL, you can then click "Downloaded File Analysis" in the result to get an actual multi-engine antivirus scan of the file itself before you download it yourself!
Aside from the obvious benefits of not having to download and then upload a file to VirusTotal, this also avoids the possibility that you might inadvertently upload a private file to VirusTotal. For example a file with your personal information that you were able to download from a site while logged into your account. By sending such a file to virustotal, you are in effect releasing it to a couple of dozen antimalware companies, which you might want to do. If using this extension, VirusTotal will only be able to access public URLs so you don't have that risk.
Sometimes it doesn't work if the "download" URL merely redirects to the actual file URL, or if it uses parameters and/or no explicit file extension. It would be nice if it could be smarter about those.
I hide the annoying toolbar. Unfortunately you can't drag its buttons or fields onto another toolbar, but I get the same functionality with two bookmarklets.
It would be nice if we could right-click on an existing download in the download manager and send its original URL directly to VirusTotal. In the meantime we can right-click on the download and Copy Download Link and paste it into the vtzilla toolbar field or an equivalent bookmarklet prompt field.
Also it would be nice if we could automatically send every download URL to virustotal while downloading it, if we don't choose to explicitly send it to virustotal before downloading. Better for virustotal to check it while or just after downloading than not at all.
How about checking the current page URL automatically in the background?
Maybe checking a link URL automatically while hovering over it for a bit? Or at least automatically checking every distinct *site* linked to on the current page (check with a site-level URL).