Ensure IE drag and drop

Sometime IE decides to ignore dragging a draggable element. You can force IE to take notice by using its nonstandard "dragDrop" method:

document.getElementById('draggable-thing').addEventListener('mousemove', function(e) {
    var target = e.target;
    if (target.dragDrop && window.event.button === 1) {
        target.dragDrop();
    }
});

(via http://stackoverflow.com/a/8986075)