HTML Validator is a Mozilla extension that adds HTML validation inside Firefox and Mozilla. The number of errors of a HTML page is seen on the form of an icon in the status bar when browsing. The details of the errors are seen when looking the HTML source of the page. The extension is based on Tidy and OpenSP (SGML Parser). Both algorithms were originally developed by the Web Consortium W3C. And now extended and improved by a lot of persons. Both algorithms are embedded inside Mozilla/Firefox and makes the validation locally on your machine, without sending HTML to a third party server. Each algorithm has advantages and inconvenient.
||Firefox 5.0 - 9.0