Vertical tab bar shouldn't move the page when changing between hidden and visible
If you autohide the vertical tab bar it moves the page when shown. It would be A LOT better if it instead could show over the page (overlay) and keep the page in the same position as it is.
Tree Style Tab has the same problem with resizing. It greatly slows down switching between tabs on my fairly modern netbook.
This feature is already part of 'Tree Style Tab'. I find it helpful on netbooks because of their small screen and small computing power https://addons.mozilla.org/da/firefox/addon/5890/
on my (very old) laptop, the resizing of the main page when the tab bar is momentarily shown is sometimes painfully slow. I imagine if the tab bar floated on top of the page frame the browser would have a lot less work to do to update the display.