- Find bookmarks.tpl.php and open it in your favorite text editor.
- Fidn the line containing the word "taggedlink" and add the following (inside of the href brackets): target="_NEW"
The line should look something like:
<a href="'. htmlspecialchars($address) .'"'. $rel .' target="_NEW">'
That's it. Clicking on a link should now open the listed bookmark in a new tab or window (depending on how you have your browser configured).