According to that log "Internet/ firefox.desktop /usr/share/applications/firefox.desktop", that doesn't make really sense since gnome-panel uses gnome-menus to list the items for the menu, could you make a screenshot of the internet menu (use "gnome-screenshot --delay=8" by example)?
** Changed in: gnome-panel (Ubuntu) Status: Needs Info => Unconfirmed -- applications menu doesn't show firefox https://launchpad.net/bugs/43151 -- desktop-bugs mailing list desktop-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/desktop-bugs