This website wants to run the following add-on: 'MSXML 5.0' from 'Microsoft corporation'

Without going into great detail, there is a simple fix for this.

Problem: One of the javascript files, sarissa.js, which Plone uses for assistance with Internet Explorer's XMLHTTPRequest object, is out of date.

Solution:

Download the latest version of sarissa.js
Locate the sarissa.js file, which can be found in the zip file at /gr/abiss/js/sarissa, obviously!
Copy this file into the following folders on your Plone instance (overwriting the old sarissa.js):

/products/archetypes/skins/archetypes/archebuilder/sarissa.js
/products/CMFPlone/skins/plone_3rdParty/sarissa.js
/products/FCKEditor/skins/fckeditor/sarissa.js (if you have FCKEditor installed)

Restart zope

Alternate solution:

Go to portal_skins -> properties in the ZMI
Make sure that FCKEditor skins are placed very last in the list

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