TST Hoverswitch от Klemens Schölhorn

This add-on for Tree Style Tab allows you to switch the current tab just by hovering over it with your mouse (moving the mouse cursor over it). You can configure the delay between hovering over the tab and actually changing to it.

Screencast

You need at least Tree Style Tab 2.5.3 and may have to reopen the tab bar after installing the add-on.