While newer versions exist, the 0.9.22.3 release is frequently cited in community guides for its stability and specific compatibility:
The tool acts as a bridge between a Windows PC and an Xperia device in "Flashmode" or "Fastboot mode" to perform the following: Flash Stock Firmware : Install official Sony firmware (in Flashtool-0.9.22.3-windows.rar
Comprehensive Guide to Flashtool-0.9.22.3-windows.rar for Sony Xperia While newer versions exist, the 0
Turn on your phone. The first boot after flashing can take significantly longer than usual (5–10 minutes). While newer versions exist