HTML Validator extension for Firefox and Mozilla                             

FATAL ERROR : The dynamic C library  contained in the extension file could not be found.
Cause 1 : Operating System mismatch Cause 2: Linux / Cause 3: Windows Vista / Cause 4: Seamonkey upgrade
Cause 5: Browser / Cause 6: Other / Uninstall instructions

Cause 0 : since 27-SEP-2011, there is a bug in

The Windows version 0.910 is declared compatible at with Firefox 7.0 but it is not.
No way for me to change this, it is all automatic... There is a bug logged for this.


Download the version 0.911 for Windows 
or look the compatibility list
or wait that solves the issue...

Cause 1:  Operating system mismatch

This can happen when you have installed a version that is not for your Operating system (OS). For example, installing the Linux version on Windows or the opposite. The extension is available on Windows, MacOsX, Linux 32bits, Linux 64bits and Linux PPC. This happens mostly due to bad autodetection of the OS or caching issue in

Solution: re-install the extension for your OS.

  1. Please, look at the list of OS here, and install the version for your OS. Take care to allow this site to install an extension (green toolbar at the top)
  2. Retry in and take care that the version installed is the one for your OS.

Cause 2: Linux 

A. On linux, depending of your linux distribution, it can be that the standard C++ libraries installed on your distribution are not the one linked with the extension. To correct this, please read the detailed info, here:

Take also care that the extension is different for Linux 32bits (most common), Linux 64bits and Linux PPC.

B. In an update on Debian from about June/July 2006, solved in about August 2006. The extension does not work on Debian anymore. The reason is the way debian has changed his way to link the XPCOM library in Firefox.

Cause 3: Windows Vista

You need to be administrator to install the extension on Firefox in Windows Vista.

Cause 4: Seamonkey upgrade

When reinstalling a new version of Seamonkey on an existing one, Seamonkey warns that it will deregister all components. Practically, the library of the extension is deinstalled. To solve this, just reinstall the extension.  Download here

Cause 5: Browser (Netscape 7.x, 8,x, Seamonkey 1.0.x)

Like told in the download area, the extension has been  tested on Firefox, Mozilla Suite 1.7.
It is reported to work on Flock without any issue.

It does not work on Seamonkey, nor on Netscape 7.x or 8.x.
If you use these browser please deinstall the extension. See below.

Case 6: Other

Check the forums

If you do not find an answer, add your question in it .
Then contact me if you do not find a solution : Marc Gueury :

To uninstall the extension:

In Firefox, Flock,
- go in the Tools/Add-ons menu (called Extensions in previous versions)
- choose HTML validator in the Extension list
- click uninstall
- restart Firefox.

For other browsers, see

Additional info:


 In the Java console, you will see this error message
Error: Components.classes[';1'] has no properties
Source File: chrome://tidy/content/tidyUtil.js
Line: 96