To enhance the Firebird functionality, IBSurgeon has sponsored the development and now released for public use the free open source "IBSurgeon Full Text Search UDR" to perform full text search queries within SQL and PSQL. UDR works with Firebird 3 and 4, for Windows there are ready-to-use binaries, for Linux it is necessary to build the UDR.
The UDR is based on Lucene++ engine, with all the powerful features required for full text search and with very fast performance (build as native C++ library).
The binaries of IBSurgeon Full Text Search UDR, its sources, and documentation are available on GitHub https://github.com/IBSurgeon/lucene_udr
And don't forget to mark it with star on GitHub!