Dr. Web helps you minimize contact with unsanitary files before you download them, by scanning them in advance and letting you know if the file has a clean bill of health or if you should put on your biohazard suit before handling the innocuous-looking critter.
This review is for Firefox and Thunderbird, although the publisher makes versions for Internet Explorer and Opera, as well. The plug-in adds a context-menu option that scans files for viruses before you download them. It then opens up a new window, and even with a 400MB file it took only about 15 seconds to return a green-themed "Clean" window for a virus-free result. The red-tinted "Infected" pops up if you're about to perform some risky behavior.
One thing to keep in mind with the link checker is that it's designed only to check for viruses and it's only meant to work with downloads. Dr. Web's effectiveness depends on how often its publisher updates its definition files, but since the publisher's been around since the mid-1990s it seems to take its updates very seriously. The plug-in doesn't do much beyond what's advertised, but what it does fill a small but important hole.
Dr.Web Anti-virus Link Checker allows you to check any file you are about to download, any page you are about to visit with online version of Dr.Web anti-virus. New menu item "Scan with Dr.Web" will appear on hyperlink context menu. This version is the first release on CNET Download.com.