Note: If you are using Wordpress or another Publishing system and it’s not working as intended you may need to load it from a different file. Simply make a open-all-links.js file and load it from your header.

<script>
onload = function() {
    var frame = parent.frames[0].document;
    var links = frame.getElementsByTagName('a');
    for (var i=0; i<links.length; ++i) {
        links[i].setAttribute('target','_blank');
    }
}
</script>