Permission denied to call method XMLHttpRequest.open

Problem
When deploying DHTML OpenLaszlo applications in SOLO mode, attempts to fetch datasets results in the following error:

ERROR: uncaught exception: Permission denied to call method XMLHttpRequest.openLFCdhtml-debug.js (line 1421)
uncaught exception: Permission denied to call method XMLHttpRequest.open

Solution
As a security measure, most browsers restrict XMLHttpRequest such that they don't accept XML data if the HTTP response headers are not properly set. To fix this, simply change Content-Type to:
Content-Type: application/xml; charset=UTF-8