Specifically "firefox-92.0.1-1.1-aarch64.pkg.tar.xz" .
Not sure how to report directly to the mirror maintainer, but it seems to be on all other mirrors:
IE:
http://il.us.mirror.archlinuxarm.org/aa ... pkg.tar.xz (404)
http://ca.us.mirror.archlinuxarm.org/aa ... pkg.tar.xz (200)