Update Rated 5 out of 5 stars
From my earlier review: I've really enjoyed using Vertical Toolbar, which should've been part of Firefox by default ever since wide screens became the norm. Even though I use a 23" 1920x1080 LCD, switching just 1 toolbar to vertical made a noticeable difference, so I imagine it'd be excellent on a small screen.
Update: My earlier review said that I gave it only 3 stars because of two problems: it was making my icons revert to the built-in blah gray style, and that adding the Bookmarks Toolbar Items disabled the ability to customize toolbars. I let Firefox spend a few restarts (one wasn't enough) with the Vertical Toolbar disabled, then when I enabled it again, the problems were both gone: my themed icons are back & I could customize toolbars despite the Bookmark Toolbar Items being on the Vertical Toolbar. So, now I'm giving it the 5 stars it deserves since everything is working. :)