I checked result data and comproved that is in utf8 format. So I think
the problem is in php data handling right?

Now I got a question, I think php app proces data in utf8 way, but how
is written to firebird if connection uses ISO88559_1 charset? May be
data from web must be processed with utf8_decode() prior to save at
databse, and then encode again to show again.

I would do a test with utf8 encoding/decoding data within php and
confirm my suspect.

Thanks.
Julian.