I just started using Firebird a couple of months ago.  I have Helen's book and Google.  I didn't have any trouble finding information/documentation.  I tended not to use Helen's book, just because it required more muscle strength to lift it than to type a query into Google.

Maybe I'm not using Firebird's advanced features.  But I was using it with isql, ODBC and Python FDB driver.  I had to understand collations, create triggers, views, sequences, procedures. some UDFs, indexing, stats, blobs, server/embedded.  So it's not like I just used an ORM to ignore the database, and just dumped stuff into tables.

I only needed to ask 1 question on the support group.  And I got a speedy reply which made perfect sense.

So, I think for new users, it can't be that difficult to find information (I assure you, I'm a lot dumber than most programmers).  Maybe it is more of a problem to find information if the user is not a native English speaker, or is searching for information in another language.  Granted, I've got some experience with other databases.  But when I've used Postgresql in other projects, I've struggled more to get things working than with Firebird, and struggled more to find documentation which explained what was causing problems for me.

I suspect that Firebird might have less hype about it than other database servers more because of "specialisation".  Server-side programmers will be concerned with Postgres/MySql/Oracle; embedded programmers will be more concerned with sqlite/express versions of proprietary DBs.  Because Firebird straddles server/client-server/embedded (and cross-platform, at that), the enthusiasts are going to be spread across different specialisations (on the whole).