To work around this behavior, follow these steps:
Press Alt+Tab until the running app that you have to debug is selected.
Use the mouse to pause the pointer on the element that you have to debug, and then click the element to select it.
Press Alt+Tab to switch back to the DOM Explorer in Visual Studio 2013 Preview.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.