There seems to be a bug in the following Menu Wizard Firefox extension.
Menu bar > Bookmarks > Bookmark this Page > Properties > Keyboard shortcuts > uncheck this option.
Menu bar > Bookmarks > Show all Bookmarks > Properties > Keyboard shortcuts > uncheck this option.
After unchecking both of the Bookmarks options and restarting Firefox, the options or keyboard symbols remain visible in the Bookmarks drop-down menu.
If possible, thanks for fixing this bug.