You can add this to your Custom JS to force all anchor tags to open in a new tab:
jQuery(".ms-formbody").on("mouseover","a",function(){
jQuery(this).attr("target","_blank");
});
If you only want to target one specific field you can change it like this:
jQuery("#dffs_YOUR_FIELD_INTERNAL_NAME_HERE").on("mouseover","a",function(){
jQuery(this).attr("target","_blank");
});
Alexander