Můžeš zkusit toto:
Případně se podívej sem:To perform the ultimate lock on Firefox into opening everything in one window in tabs, open about:config and set the following prefs:
browser.link.open_external set to 3 (should already be)
browser.link.open_newwindow to 3
browser.link.open_newwindow.restriction to 0 (zero)
http://support.mozilla.com/cs/questions/749234
http://www.j79zlr.com/howto.php?id=17