I love this addon so much. It's 90% of the reason I use FF over any other browser.

It's a must-to-have!
Would it be possible to add an optional vertical scroll bar? Or a way to speed up scrolling using the mouse wheel (w/ a key modifier), at least? It may take ages to scroll from bottom to top tabs when there's a lot of tabs.

Initial testing is good. On first install, it doesn't look like to captures the current tree-state of the open tabs (may be my setup?).

Still to see if closing a tab in the intermediate tab stack loses the tab connections (may need 'Tab flip for Tree Style Tab'?).

Have tried the closing of an intermediate tab and it shrinks the tree, rather than remembering the call stack.