Currently there are only 2 choices for size of vertical tabs area. It can either be minimized (which defaults to auto shrink) or pinned. Is it possible to enable resize when the vertical tabs are pinned? This behavior is supported in the Tree Style Tabs Firefox extension. This extension is the gold standard for vertical tabs.
It would be great if the panel could be resized in both hover and pinned modes. Even better would be having the size retained independently for both modes of operation. I would prefer during hover that the panel be wider to show more information about the tabs because it is sliding out over the top of the current page anyway. When pinned I would prefer to have the width smaller so that it takes away less horizontal space from the active page.