try something like this:
var lastBoxedEl;
function moused(e) {
var target = e.target; //experiment, try e.currentTarget, e.originanalTarget
if (lastBoxedEl) {
lastBoxedEl.style.outline = 'none'
}
lastBoxedEl = target;
target.style.outline = '5px solid red';
}
document.body.addEventListener('mouseover', moused, false);