Rated 4 out of 5 stars
It's perfect for those with a widescreen monitor or those that value vertical space over horizontal. However, there are performance issues (it seems slower than the default arrangement, but this can be resolved by turning off tab animations via about:config) and the extension lacks some built in settings that I believe are essential (e.g. colour scheme, single click to open new tab, moving the new tab button to a fixed position at the bottom). Include more customisability and this would be 5 stars.This review is for a previous version of the add-on (0.14.2013100901.1-signed).