Am I the only person that loathes sidebars in browsers? Maybe it's because I've been using a browser since 1996, but my brain is deeply set in the idea that the space below the chrome 110% belongs to user space.
I've tried a few browsers with vertical tabs, and my brain keeps seeing them as part of the page itself. It's a very distracting and uncomfortable experience.
Do you always have browsers maximized? If you're used to other windows next to the browser then I'd be surprised if you still find sidebars distracting.