If you right click on the Library button, you get a menu with three options (I'm quoting the Help screen here to describe what each option does):
• Open: opens in a floating window.
• Open in a new tab: opens as a panel on the left side of the main window.
• Open in a floating window: opens in a floating window.
The first and third of these do the identical thing. Why have both of them, then?
Same goes for right-clicking a title in the library, however in this case, Open opens in a new tab. The fact that it behaves differently from the Open in the Library button case seems random. Why not do away with the redundancy by omitting "Open" altogether from both of these right-click menus, and thus make the behavior of the menu items crystal clear, not open to guesswork?