The 2.5.9 update focused primarily on bug fixes and performance optimizations rather than introducing major SQL enhancements. Firebird 2.5.9 Release Notes
Although the v2.5 series has reached its end-of-life (EOL), you can still find official binary kits for various platforms: firebird 2.5.9 download
: The central hub for all Firebird 2.5.9 Downloads , including installers for Windows, Linux, and macOS. including installers for Windows