In case it helps in diagnosing the problem, here’s the end of the Firefly log after a crash.
2008-11-24 15:14:14 (b7445b90): Opening /usr/share/mt-daapd/admin-root/FirePlay.swf
2008-11-24 15:14:14 (b7445b90): Opening file:///usr/share/mt-daapd/admin-root/FirePlay.swf
2008-11-24 15:14:14 (b7445b90): Checking handler for file
2008-11-24 15:14:14 (b7445b90): opening /usr/share/mt-daapd/admin-root/FirePlay.swf
2008-11-24 15:14:14 (b7445b90): Emitting reponse header Content-Language: en_us
2008-11-24 15:14:14 (b7445b90): Emitting reponse header Content-Type: text/html
2008-11-24 15:14:14 (b7445b90): Emitting reponse header Server: mt-daapd/svn-1696
2008-11-24 15:14:14 (b7445b90): Emitting reponse header Connection: close
2008-11-24 15:14:14 (b7445b90): Emitting reponse header Date: Mon, 24 Nov 2008 21:14:14 GMT
2008-11-24 15:14:14 (b7445b90): Write error: Connection reset by peer
2008-11-24 15:14:14 (b6c44b90): Received a message from daap server
2008-11-24 15:14:14 (b6c44b90): Rendezvous socket closed (daap server crashed?) Aborting.
2008-11-24 15:14:14: Aborting