User Guide


1. How to use the HTML validator for Firefox
2. Tidy vs SGML parser
3. Validate now ( after JavaScript or AJAX execution )
4. Icons
5. Customize toolbar: How to change the place of the HTML Validator icon ?

1. How to use HTML validator for Firefox 

We will validate a small HTML page with just an small HTML warning. (Test yourself)

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">

We will use Tidy as algorithm. If you want to use another algorithm, go to the options. (For more info, click here).

If you open "Developer tools", (CTRL+SHIFT+I) and go to the HTML Validator tab.  you will see the warning icon in the toolbar

Developer Tools

You will also see the source of the HTML page with a warning and an explanation of that warning.

You have now 2 choices.
1. correct it yourself with the help given next to the error. Then press CTRL+R (refresh) to see if it is solved
2. Or press on the clean up button that will correct the HTML for you.


That's it ! You can try the same with the SGML parser to be sure to have the same errors than the W3c.
The differences between the 2 algorithms is explained below.

2. Tidy vs SGML parser

W3c has made 2 programs to verify the HTML syntax. Both uses different algorithms:
This extension implements both algorithms without changes. Both technologies have their advantages and disadvantages.

A. Tidy

From my experience, Tidy has the following advantages:
If you have questions about the tidy validation result, there is a user list and with archives: http://lists.w3.org/Archives/Public/html-tidy/

B. OpenJade, the SGML Parser

OpenJade, the SGML parser, has the following advantages:

3. Validate now ( after JavaScript or AJAX execution )

The extension validates by default HTML pages returned by the Web server. But the HTML of the HTML pages can changes due to JavaScript code after :
  • that the page has been loaded
  • after some user interactions,
  • or Ajax events
The extension 0.8x allows to validate a page in his current status after JavaScript execution. This option is available in the right menu of the validator icon in the status-bar

There are several technics to change a page with JavaScript: You can test yourself with the extension installed.

A. SAMPLE 1 : creation of a HTML element with DOM (Test yourself)
var doc = window.content.document;
var body = doc.body;

body.appendChild( doc.createElement("br") );

B. SAMPLE 2 : creation of HTML with document.write (Test yourself)
doc.write( "<br>" );

Here is a SAMPLE 3 (Test yourself) with a good HTML page given by the webserver but with JavaScript inserting, inside the HTML, a HTML error.

4. Icons

When using the HTML Validator extension, you will encounter some icons depending of the errors in the page. Here is the list of the icons andf their meaning.

good 0 errors / 0 warnings

This icon appears when Tidy has found no error and no warning during the validation of the page. Your page is good this is what we should all aim for.

warning 0 errors / x warnings

This icon appears when Tidy has found warnings: HTML errors that Tidy can correct using the cleanup. The error should be corrected and Tidy can propose you some change in you HTML code to fix it

error x errors / x warnings

This icon appears when Tidy has found errors: HTML errors that Tidy can not correct using the cleanup. So, you will need to correct these errors manually before Tidy can help you to correct the warnings.

warning Disabled

This icon appears when the validation is disabled for one reason below:
- the extension is disabled completely in the browser.
- or when the page is not an HTML page (ex: PDF)

exludeNot in domain list

This icon appears when the url is excluded from validation for one reason below:
- when the protocol is about: (ex: about:blank)
- or when the page is an URL defined in the exception list of URLs that should not be validated (in the Options...)
- or for some advertisements in frames (when tidy.options.validate_ads=false)

charset Error: The HTML contains invalid characters

This icon appears when the page contains some characters that are not defined in the character set used by the page. It appears typically in page declared as UTF8 but in reality stored in Latin1.

Without being able to read all characters of the page, the extension is not able to validate the page. Such bad characters appears like <?> in the HTML of the page or in the Page Source.  Here is a screenshot of one of them:

charset Html Cache is Empty

This icon appears when the HTML cache is empty. If the cache is empty, the extension is not able to get the HTML and without HTML, it is not possible to validate it ....

This appears most of the time when the HTTP return code is not 200. (ex: HTTP-404). In such case, even if the browser return HTML, Firefox does not store it in his cache. And I am not able to validate it.

Another way to have this icon is to disable the cache of Firefox in the about:config.

hidden 0 errors / 0 warnings

This icon appears when a page does not contains any errors or warnings after that a filter has been applied. And the filter hides some errors or warnings.

question  No validation result

This icon appears only in Firefox 1.0.4 and after. But not in Mozilla or Firefox 1.5 beta and always for a frame that has been validated as part of a page.

It seems that in such version, the validation result stored in the HTML frame is lost between the validation of frame itself and the validation of the parent page (that is always done after).

This is a bug but since it is solved in Firefox 1.5 beta, I do not worry to much about it. In such case, you can anyway see the validation by going to the view source.

5.  Customize toolbar. How to change the place of the icon ?

Since version 0.952, you can change the place of the validation icon in Firefox.  customize
Click on any toolbar and choose Customize...

After this, Firefox will go in a special mode where you can drag and drop the validation icon.
The icon can be placed in any toolbar.

In the navigation bar, when the icon is shown with text, the text will have another smaller format. See screenshots.

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