Simple drag/drop of images into Firepad... probably not production-ready, but seems to work.

firepad-drag-drop.js

codeMirror.setOption('onDragEvent', function(cm, e) {
    // Move the cursor as they drag.
    var pos = codeMirror.coordsChar({left: e.x, top: e.y });
    codeMirror.setCursor(pos);
    codeMirror.focus();

    var isImageDrop = e.type == 'drop' && e.dataTransfer.files && e.dataTransfer.files.length > 0 && e.dataTransfer.files[0].type && e.dataTransfer.files[0].type.indexOf('image/') > -1;
    if (!isImageDrop) return;
    event.preventDefault();

    var reader = new FileReader();

    reader.onload = function(event) {
        var img = new Image();
        img.onload = function () {
            firepad.insertEntity('img', {
                'src' : event.target.result,
                'width' : this.width,
                'height' : this.height
            });
        };
        img.src = event.target.result;
    };

    reader.readAsDataURL(event.dataTransfer.files[0]);

    return true;
});