Download: https://addons.mozilla.org/en-US/firefox/addon/249
Author Site: http://users.skynet.be/mgueury/mozilla

As mentioned before, validation isn’t just something with which to impress people, it’s also an excellent way of discovering problems which might be affecting the way your website is rendering.

In this regard, the HTML Validator extension for Mozilla Firefox has quickly proved its worth as a problem solver with an almost instantaneous report of validation errors of every website you visit in your browser.

When installed HTML Validator presents a small icon in the status bar which will either show a big red X, a yellow warning symbol, or a friendly green tick. This means that at a glance you know whether your web page is validating or not.

Obviously the green tick demonstrates that there are no errors. The yellow warning symbol demonstrates that there are warnings, which will mean that your page will pass validation, but there is some code that could be improved upon.

In the case of a red X, you instantly know that something is wrong, and with a quick double click on the icon you get a detailed analysis of where the errors are occurring in your code.

Error Analysis

Clicking on each error gives some information regarding the possible cause, as well as suggestions of the correct means of action. In addition to this, it displays the source of the code with the specific error highlighted. Sometimes the error details are a little vague, usually demonstrating a general correct syntax example which might not relate directly to the error at hand, but more often than not it helps point you in the right direction.

Possibly the only faster way to find errors is by using Joe Hewitt’s Firebug, however I have found myself returning to HTML Validator due to the simplicity of information display and the low impact this extension has on Firefox memory usage and page load times.

This tool is highly recommended.