I recently installed [V.J. Catkick@’s Twitter Plugin for WordPress][1]. Shortly thereafter I noticed my [HTML validator Firefox Plugin][2] changing from a pleasing green check mark to a nasty red cross complaining about (X)HTML validation errors.

[1]: http://www.vjcatkick.com/?page_id=5475
[2]: https://addons.mozilla.org/en-US/firefox/addon/html-validator/

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