Selecting text, then moving scrollbar button generates a prompt for Drag and Drop add-on, then hangs browser in IE8

I attempted to select text in confluence.gdev.com. I selected some text near top of page, then clicked on the scrollbar thumb at the right side of the browser to scroll down to the bottom of the page. Next, I received a message box prompting me about a Drag and Drop add-on feature. At this point, the browser hung with the perpetual hourglass, requiring that I start Task Manager in order to kill the app. Please note: clicking and dragging the scrollbar thumb is not the same as clicking and dragging selected text.