Great but hopes Development Continues Rated 5 out of 5 stars
With Firefox Development teams could care less about vertical tabs. I hope this Add on gets constant development. Chrome has a VERY good vertical tabs implementation. It has higher Height per tabs, which is easier on the eyes, the Close button is also larger. May be get rid of Scrolling Bar and have Up and down arrow at both end to indicate there are more tabs. Also Support of App Tabs although i have no idea how this should be done.
I also wonder if the Tab Bar could takes whole of side like chrome instead of just browser area under the Navigation Bar and Menu.