Can't download
Can't download
Did you check the comments in the AUR?
Also update. The whole system.
I just installed the librewolf-bin without any issue. Did you updated your system with
pacman -Syu
I would ignore the DNS for now, unless you have a piHole or some other custom DNS service. If you want further help please copy the terminal messages when trying to install librewolf-bin and the gpg keys.
Arch Linux documentation will warn you about AUR. Other people will warn you about snaps. Some other people will warn you about flatpaks. Same for AppImage.
In my opinion it is fine to use LibreWolf from Flatpak which btw gets a blue mark. Consider editing your post title and add [Solved].
AUR appears to be quite popular but sometimes software is flagged out of date or it is dormant because the maintainer has no time any longer and new maintainers may come and go. Basically anyone can upload to AUR and there is no curation. Of course you can look at entries in the AUR and see when software was submitted for the first time and how many people have upvoted it but even that can give a false sense of security. The disclaimer at the AUR is clear : DISCLAIMER: AUR packages are user produced content. Any use of the provided files is at your own risk.
Flatpak has a drawback of pulling in more software that an application depends on (For example GNOME or KDE libraries) and someone has made a website flatkill.org of their bad experiences with Flatpak but that is from 2020. In the mean time there is Fedora Atomic desktop flavors depending on using Flatpak.