Scroll bar for the sidebar for laptop users and broken middle button users

[pf333333]

Can you add a scroll bar to the settings, doesn't need to be enabled by default, and doesn't need to appear unless the sidebar is fuller, but having it available somewhere would help out.

I remember there was some addon somewhere online, might be a firefox thing, but I think this should be something integrated within Zen, at the very least in the settings, since enabling it by default isn't really necessary in my opinion.