extracted from bug 8123:

what I'm proposing is that a new menu entry, full menu, be added.  Full menu
takes you to the top of the complete, uncustomized, menu tree.  Full menu is
pinned, in the sense that it must be on the customized home menu.

The point is that one of the down sides of a customized menu is that you
occasionally need one of the entries you've disabled.  To use it, you have to
first re-enable it, then use it, then disable it again.

So a full menu entry would avoid that nuisance, and would also serve to
guarantee that you could get back to the customize home menu part of settings,
since settings it under full menu.  Thus, full menu can replace settings as the
only entry that the customized home menu is force to contain.