Very Good One except .... Rated 5 out of 5 stars
A mandatory add-on if you have a lot of tabs open and reopen at start-up. Before I use TabKit, but the developer did not update it since 1 year. On Firefox 4 or 5, this is the only solution for those who need vertical TabBar. The only problem is it is slowing the start-up time by 62% (see: https://addons.mozilla.org/en-US/firefox/performance/ ). The developer is very reactive and I hope he would soon correct this.This review is for a previous version of the add-on (0.12.2011061701.1-signed).