Still needs work, many things don't work! Rated 3 out of 5 stars

It could be 5 star but:
1- There are missing keyboard shortcuts -collapsing/expanding should be done easily by keyboard.
My suggestion: ctrl+alt+left/right arrow without the need to focus on them. this way it doesn't conflict with ctrl+arrow shortcut of Firefox for moving tabs when the focus is on them.
-moving up and down the main trees must be doable by keyboard. My suggestion :ctrl+shift+page up/down

I use the top (default bar) and these functions don't work:

2- holding controle for unhiding the tab bar
3- "when tab get focus, exapnd it's tree and collapse others"

help and documentation is missing.
example: what is the difference between these two?
the next sibling of the current tab
a sibling of the current tab

Thank you

This review is for a previous version of the add-on (0.14.2012122901).