add a user-configurable shortcut (and possibly a menu in the app main menu Window section) to focus on the last tab.  This could be an Alt-0 or Alt-9 (the latter is from Firefox)

we need to change our hard-coded Alt-0 through Alt-9 key handling

also, there is no key mapping collision detection between shortcuts programmed via File -> Options and hard-coded key strokes.  I am not sure how to fix that after the fact because there are so many of those hard-coded key strokes and they are scattered across the code.