The site wants Firefox to install the MSXML browser plug-in: why?

The MATC site is built on the Plone CMS. Plone requires the MSXML plug-in to perform certain tasks with Microsoft's Internet Explorer (IE) web browser.  If your Firefox browser is configured to identify itself as IE (which it can do for compliance with sites that refuse to work with any other browser), then you will see a message indicating that Plone is attempting to install MSXML. Firefox isn't able to install that plug-in, so it will complain. To solve the problem, you can turn off IE emulation, or use IE if you're running Windows.