HTML Validator is an extension for the Firefox open source browser which provides all necessary tools for the validation of Web pages, the plugin is based on OpenSP Tidy and two algorithms developed by W3C (World Wide Web Consortium) that is consortium that sets standards for the Web.
HTML Validator is installed like any other extension, but it offers unique features, it fails to detect errors in the HTML markup that does not recognize same Tidy generally also support the parser OpenSP can give the same results guaranteed by the validator W3C.
Translated into several languages, HTML Validator also incorporates a feature called Clean up that allows you to automatically offer an alternative version, with no errors and validated a Web page.