Recently, we came across a website (http://validator.w3.org/) offering WC3 validation, which basically checks a webpage for html errors.
This is a great free tool as now we can validate our html and make sure that there are no html errors present in our webpages.
It did not take long to find a plug-in for Firefox which uses the same parser as http://validator.w3.org/, but with a few extra advantages, like being able to validate any page that you can display in Firefox.
In the past, we would use a browser to display a page we wanted to check for errors and if the browser returned no errors, then that was that. Unfortunately, web browsers are designed to silently recover from common html errors, so they show no errors when there could be html errors on a page!
We have already fixed hundreds and hundreds of html errors in our code and will continue to fix any html errors that we come across in the future, using Html Validator 0.8.6.1.
Please feel free to contact us with any questions you may have.