krakn [1] filed a deletion request for firefox-moonlight [2]: Quoting the official website (http://www.mono-project.com/Moonlight):

Note: Moonlight isn’t actively developed anymore. If you’re feeling adventurous you can probably get it working by compiling from source, but we recommend you move away from Moonlight as soon as possible.

[1] https://aur.archlinux.org/account/krakn/ [2] https://aur.archlinux.org/pkgbase/firefox-moonlight/