I think mostly that it is not part of the UI. Functionality wise I think it is ok.
Basically:
- the original tabs are still displayed (I know there was some way to tinker with FF files to have them hidden, but now I can't find where I've seen it)
- when viewing bookmarks, the treestyle tab disappears (since it's using the same side bar), so then need to use F1 to get it back)
- the old version also had an option where the side bar shrunk, and expanded when you hovered mouse, saving some space.
Basically:
- the original tabs are still displayed (I know there was some way to tinker with FF files to have them hidden, but now I can't find where I've seen it) - when viewing bookmarks, the treestyle tab disappears (since it's using the same side bar), so then need to use F1 to get it back) - the old version also had an option where the side bar shrunk, and expanded when you hovered mouse, saving some space.