To disable the popup you would have to open up the PowerGallery/galleries/ribbon_fullsize/js/gallery.js file and find the block of code that starts with:
//tooltips
and comment it out, so it looks like this:
//tooltips
/*this.tips = new Tips(this.thumbs.images, {
className: 'pg-rf-tip',
<additional code here>
this.tip.setStyle('top', '0px');
}
});*/
This will disable the mosueover popup for ribbon + fullsize only. If you decide to change the design you will have to make additional modifications.
