I found it to be pretty solid and fast when I last used it, which was right after Borland Open-Sourced it. It was forked from Interbase.

Firebird seems stable and fast enough, what it does lack is good client libraries. We looked at different database solution when rewriting our current webshop and Firebird was something we looked at, but because we're a Python shop we dropped it. I'm not saying that the current Python driver doesn't work, it does, but it doesn't seem to be updated very infrequently and it's still seems more like an InterBase driver than a Firebird driver. We went the Postgresql route, and why really, why wouldn't you?

Don't get me wrong, it's a great database and I know a company that use nothing else and won't switch if you paid them, ( They are use .Net ).

I wrote an accounts receivable/payable app in Borland Delphi back in 2002. At the time Interbase was the easy choice. At that time, Interbase was transitioning to Firebird. I dropped it in as a replacement and it did its job fine. If you like MySQL, you'll miss auto incrementing Primary Key Columns that MySQL seems to have made so popular. It's not too hard to setup a trigger for sequence types, but it's not built in. (or it wasn't back then) All the tools for management were the Interbase tools. Most of my stuff is either MySQL these days or Postgres when I need good spatial support. I've messed with CouchDB a bit. I just don't see Firebird going anywhere for my needs.

But they could happen in the future to work for a corporation that would like to pay, but as it stands they will never suggest using MySQL. Thus MySQL will slowly disappear from the youngs mindshare and Oracle will make no money at all on it.

How many people use a SQL DB without some form of support contract?

To do so is not too smart if your business relies on the DB to function.