CSS Validator for Windows

Instead of offering a way to validate CSS on its own, this free Firefox add-on is really a link that directs you to the W3C Web site.

You'll find the link in your context menu. Just visit a Web page, and, if it contains an associated-CSS file, you can click on the Validate CSS link. It then opens another tab in your Firefox browser to display the CSS information directly from the W3C site, including any errors found. It worked without issue for us.

If you're a Web developer, this free add-on will save you the extra step of having to manually enter a URL each time you want to validate a Web page.