Well done, one needed addition Rated 4 out of 5 stars
Positive Review, however, Vertical Toolbar Needs as of version 0.2.1:
Needs to be able to duplicate Icons already supposedly in use by system, and optionally place them into the Vertical Toolbar area via dragging. Prime needed example is the Reload Current Page icon ("right rotation arrow circle") that Firefox already uses to the right of the URL address dialog strip in the main FF4 program.
Sometimes a dire need that this particular Icon needs to be ALSO place-able into the Vertical Toolbar, while still also remaining usable in its other location.
Overall, Vertical Toolbar is a VERY good idea, and is well on the way to becoming one of the most popular FF tools and add-ons.