thanks for quick answer Rated 5 out of 5 stars

undo close tab button firefox add on,
https://addons.mozilla.org/id/firefox/addon/undo-closed-tabs-button/?src=ss

This review is for a previous version of the add-on (1.1.0.1-signed).  This user has other reviews of this add-on.

Ah i see! But sorry what's the problem with it? Is it supposed to show in the navigation bar rather then the tab bar?