rem: this.setLeft((d.getClientWidth() / 2) - (this.getBoxWidth() / 2)); this.setTop((d.getClientHeight() / 2) - (this.getBoxHeight() / 2)); 
add: var left = (d.getClientWidth() / 2) - (this.getBoxWidth() / 2); var top = (d.getClientHeight() / 2) - (this.getBoxHeight() / 2);  this.setLeft(left < 0 ? 0 : left); this.setTop(top < 0 ? 0 : top); 
context: proto.centerToBrowser = function(){  var d = window.application.getClientWindow().getClientDocument();  this.setLeft((d.getClientWidth() / 2) - (this.getBoxWidth() / 2));  this.setTop((d.getClientHeight() / 2) - (this.getBoxHeight() / 2));};
meta: 1005	/local1/tlutelli/issta_data/temp/all_js/javascript/2006_temp/2006/1005/141e6c5e7a855da76c4afcf02659e58ff45035e4/QxPopup.js/buggy/qooxdoo/source/script/widgets/QxPopup.js