Thank you for the answers.
So I think I will move to FB 4 after Christmas.
Yes, I use a server based FB now. But it would be nice to copy all my work to an USB-stick and put it into my pocket. The VM with the drivers etc. is rather huge, and the copy process takes its time and its space.
Why do you prefer SQLite? Firebird is really slim and powerful. And it works already.
Personal preference (like pretty much everything in life. I'll never understand why people like Hip-Hop-Music).
And: at least to me, it appears, that SQLite has a much bigger User-base than FB, so finding support for SQLite appears easier.
But that's my impression. Might be completely wrong.
And i don't/won't say, that FB is a "bad" DBMS, since i really don't have that much experience with it.
OTOH, since i have to handle different DB-"Formats" on a regular Basis (IBM DB2 on an iSeries at Work, sometimes "misusing" Excel-Worksheets as a DB-Table, CSV's, SQLite for config-Stuff and privately, MySQL privately), i've changed my "approach" how to handle Databases.
I've worked out a systematic for me, which basically can be summed up with "Shoot and forget", independent which DBMS is on the backend, without having to change a single line of code in my Frontend, if the backend gets changed, say from SQLite to MySQL to PostGres To MSSQL To DB2 To my dirty socks, whatever.