Superb. I'm hugely impressed by amount of features, details and configuration options in this extension. Used Tree Style Tab for months and now Sidebery is my extension of choice.

There is only one (but quite big) issue with usage of this extension, but it's not really fault of the author. Lack of customizable keyboard shortcuts, especially being able to bind switching to next/previous tab to something like CtrL+Q/Ctrl+E. That's an absolute shame for Firefox that it doesn't allow that.