Why not just installing the xpi-file for Firefox directly from the mono project? It works really great. Ok, it's not compiled from source, but it's available for i586 and x86_64. See here: http://www.go-mono.com/moonlight/ Daniel
I am using Opera! Moonlight works really great with Opera too. I just missing it in the Archlinux stable repo's extra. Daniel you maintain Mono, maybe you like to maintain moonlight ;)