How about:

"Firebird: A database to store your own."

With this slogan, I'm parting with the functional aspects and promoting
emotional aspects. In the spirit of "a database to call your own", I
think it conveys different meanings:

-control your own destinity (open source)

-it's YOUR data, it's YOUR database (no vendor agenda)

-clearly establishes that we're talking about a database; avoids the
browser confusion.

-conjurs the imagination, because the mind wants to finish the statement
(your own what? customers? products? history? CD collection?)

-personalized feeling; there's an implicit notion that if it's my own,
then it must be good (most minds are self-promoting). It's also a warm
welcome for anybody who hasn't used Firebird before. It think that's
important because an important goal of the project is to increase mindshare.

-scalability: my "own" can refer to my personnal data, or can refer to
my company's professional data. I think the slogan scales the same way
the database does.

alex