Duplicate Tab Blocker 0.1.0.1-signed No Restart
Prevent duplicate tabs. Allow only one tab for a url. If you click a link that is already opened in a tab, then existing tab would be focused instead of opening a new tab. This works even across firefox windows.
This add-on has been preliminarily reviewed by Mozilla. Learn more
This add-on is not compatible with your version of SeaMonkey because of the following: