After experimenting with the vertical tabs feature, I have some suggestions for friction points to my adopting this feature fully:
1) New Tab button should be at the top of the vertical tabs bar, instead of the bottom. I tend to default to the keyboard shortcuts, but it highlights the few times where I'm actually using the mouse for UI navigation and expect the button to be at the top, only to find it at the bottom.
2) New tabs should (optionally) appear at the top of the list, not at the bottom. Intuitively, I don't expect my new tabs at the bottom of the window. I expect that towards the top of the window with the rest of the UI. An option to have newest tabs appear first would be preferred here. I tend to have a *lot* of tabs open in any particular window, this results in long travel distance on larger higher-resolution monitors (e.g. 1440p @ 27inches).
3) When switching between vertical and standard tabs, the Vertical Tabs button changes location after being clicked. Ideally, this should remain in the same location after being clicked, rather than moving.