Надстройка для FF позволяющая проверить страницу на соответствие стандартам

Html Validator for Firefox and Mozilla

HTML VALIDATOR (based on Tidy and OpenSP)
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.