Rated 3 out of 5 stars
Maybe there was an "added value" to this add-on before, but now it is just a repackaged copy of workaround add-on attached to bug 469082. It does work, provided you supply proper values. The values that work for me are:
browser.link.open_external = 2
browser.link.open_newwindow = 3
(don't bother with extensions.tabsopenrelative.linksonly)
Three stars are a credit to author, hoping he will make good on his promise to keep this add-on up to date. Again, as of now this is a straight copy of someone else's work done back in April 2009, plus incorrect default preferences values that make it unusable "out of the box".