Rated 4 out of 5 stars
Just downloaded and started using. Outstanding idea, I like that I gain back some vertical real-estate with lots of tabs open.
One Feature Request to consider: I use pinned tabs to act like web apps which are always open. In TST, pinned tabs shrink to their favicons and line up horizontally at the top of the list, and they become difficult to click on because they're so small (same size as normal Firefox tab, but in a normal tab there's some extra 'tab space' around them giving them more area to click). Would be awesome if you could treat pinned tabs a bit differently: Possible ideas are a larger icon (preferred) or to still show them each on their own line like normal tabs but with some other distinguishing feature to note that they're pinned.