After more than a month of switching back and forth between Safari (my normal web browser) and Firefox to view XML data I stumbled across the following quite literally by accident. I had even gone as far as installing the Safari plugin for viewing XML which had a bad habit of rendering normal pages that contained XML as elements/attributes. And it wasn't easily disabled.
1. Under Safari Preferences go to the Advanced menu and select "Show Develop menu in menu bar"
2. Go to a web page containing XML data such as http://cortex.xiotech.com/query
3. Under the Develop menu on the menu bar select "Show Web Inspector"