Disabling browser and email client plug-ins cannot stop virus payload that come through other file types. For example, an image file (GIF, JPG, PNG, etc.) is automatically opened and displayed when an HTML document contains an <IMG> element. Image files can contain virus payload, too. This means just going to a web page that embeds a virus-infected bitmap can infect your computer! clamfs will detect the virus as long as the browser is set up to use a clamfs mount point for caching. Use the URL about:cache to find out where Firefox caches files.