Work-around for missing download button (thanks Rosa)
...(display YouTube video page)
Tools > Browser Tools > Web Developer Tools (or ctrl-shift-I)
Inspector (tab)> Search HTML (field)> #eytd_list (press enter)
...(displays 1 of 2)
(press enter)
...(displays 2 of 2. box at right: element display: none)
highlight "none" > change to "block"
...(displays popup upper left with download options)
select an option
...(displays "Save As" dialog)