Unlike Grisoft LinkScanner (Pro and Lite), McAfee Site Advisor (for Internet Explorer and Firefox), or the NetCraft Toolbar (for Firefox and Internet Explorer), this extension, published by Web of Trust (WOT), relies on user-generated ratings seconded by Web-gathered statistics to determine key factors of site safety. Trustworthiness, vendor reliability, privacy, and child safety are the four vectors of participant voting. A lengthened color gradient from green (safe) to red (unsafe) offers five shades of ratings levels instead of the customary three.
Like the other site-rating tools, WOT surfaces ratings on the browser and from within Google and Yahoo search results. There's also drop-down menu for rating sites from the search results page.
Extra context comes by way of a reputation scorecard that averages total users' ratings, a link to Alexa statistics, user comments, and spam, fraud, malicious software, and customer service complaints. According to WOT's Web site, it also garners some ratings from phishing and scam databases.
The extra user information is useful, particularly if you're a more adventurous Web surfer, and it could indeed help guard users against zero-day security breaches for users who can attribute a compromised site to a malicious software attack in time. I'd recommend the extension as a companion to one of the algorithmic solutions above, but not necessarily as a replacement.