Similar to Alt providing users access to the menubar, when the menubar is hidden in the tabbed Notebookbar, Alt could provide access to the Notebookbar tabs.
Yes, but rather than <Alt> mod-key accelerators, some could/should be provided as short-cuts.
By default the ALT focus (Alt + F for menubar file) is on the menubar, in notebookbars you can turn off the menubar and it would be very usefull that - if menubar is turn off - the focus will move to Notebookbar. If the menubar is on than the ALT focus is at menubar.
*** Bug 156895 has been marked as a duplicate of this bug. ***