I have installed from source Firebird 2.5 in the new free (for one year only) micro instances from Amazon

But you can install firebird from tar.gz or rpm (seems that basic linux installed there is based on Centos) after that the sky is the limit : django , ruby , php or why not extjs pascal web servers

Don’t forget about the replication and backups 😉 This seems to be better than google GAE or microsoft hosting: no limits on number of database or number of queries

ps:you can connect securely to firebird by creating a ssh tunnel