I have two suggestions as pertains to this topic. Please note that in both instances I am talking about the vertical tab mode although (2) could also be applied in the horizontal tab mode
Option to bring the new tab “+” button upwards so that this comes immediately after the current list of tabs.
Why? The simple case is that this will dramatically reduce mouse travel time. In the horizontal tab mode, it is natural that the “+” for new tabs comes immediately after the tabs, not at the extreme right hand of the window, so it is odd that the new tab “+” button is at the extreme bottom of the vertical tabs window. It is not intuitive and it is certainly something I find myself thinking about constantly while using the browser.
I would suggest that there be a mini “+” button when we hover in the space between two tabs to easily add a new tab between two different tabs. This is going to be a much better solution than creating a new tab and then drag and dropping it in preferred place.