Evaluating open-source DBs -Firebird Enterprise ready ?

The thread is on joelonsoftware.com and the question is about open source databases  :

Quick issue, everyone.  My company currently uses SQL Server, but we’re going to look at open-source databases because of MS’s crooked licensing rules (to be honest, they only have one SQL license, and are running it on a two-processor machine).  They don’t want to shell out the extra $6,000 for another one, and I don’t blame them.

We need a reliable database for handling lots of data (e-commerce site with about 70,000 products).  The ability to use stored procedures is a big thing.  Although it’s not a huge deal, it’d be nice to be able to automate jobs for maintenance/updating (product stock, for example).  I’m aware of both MySQL and Postgres, and a few others that don’t seem to be “enterprise-ready” as it were (Firebird?  SqlLite?).