This page describes an easy way to validate HTML documents using CSS HTML Validator and Firefox.
See also: Validating a DOM with Google Chrome.
Unfortunately, the options below are currently outdated and do not work with current versions of Firefox. We hope to find other solutions. We have kept the outdated options below in case they are still useful for any reason and for reference.
Note: Unfortunately this add-on is not currently compatible with Firefox Quantum and is no longer available.
The Firefox Easy Copy add-on extension by Byron (no longer available) can be used to quickly copy the HTML source of a web page (generated from the current state of the DOM) to the clipboard by selecting its Easy Copy->HTML Source menu option. When the document source is copied to the clipboard, CSS HTML Validator can automatically detect it, paste the clipboard text into a new document, and validate it.
Run CSS HTML Validator and then go to the Editor Options (Ctrl+F3) and select the Clipboard options page. Enable the option to Watch the clipboard for HTML documents. You may also want to enable other options like the Auto validate documents from the clipboard option.
TEST IT (v17+): If CSS HTML Validator is running and the option to watch the clipboard is checked, then CSS HTML Validator should automatically open a new document with the line "Success" when you copy the below line to the clipboard.
<cseclip url="http://test.domain.com ">Success
Take advantage of the special cseclip tag in v17+ by setting the template for HTML Source to:
The template can be changed in the Easy Copy Options dialog (Easy Copy->Options). This will allow for better recognition of HTML in the clipboard and for link checking of relative URLs (because the absolute path can be computed).
If you're using the cseclip tag, then you may want to enable Limit to only documents starting with the special cseclip tag in the Clipboard page of the Editor Options (Ctrl+F3). Using this option can prevent CSS HTML Validator from opening unwanted clipboard text that would otherwise be recognized as a document and opened in a new tab.
You can setup a new menu item specifically for CSS HTML Validator by clicking the New button in the Easy Copy Options dialog (Easy Copy->Options). See the screenshot below.
Note: Unfortunately Firefox's current framework now makes it difficult, if not impossible, to call native programs. Because of this, this add-on no longer supports CSS HTML Validator.
The Firefox Html Validator add-on extension by Marc Gueury (new window) supports recent versions of CSS HTML Validator (v10.02 or greater, any edition). In the Html Validator add-on's options dialog, choose CSE HTML Validator for the Algorithm (highlighted in the screen shot). View the page source to see the validation results.