nicman23 [1] filed an orphan request for thunderbird-appmenu [2]: i am willing to take it up. i have thunderbird 78 with appmenu working in my machine using unity menubar patches from firefox.
[1] https://aur.archlinux.org/account/nicman23/ [2] https://aur.archlinux.org/pkgbase/thunderbird-appmenu/
