This firmware was particularly notable in the modding community because it patched the WebKit exploits used by earlier jailbreak methods. If you're considering homebrew, 9.00 is generally not the version you want (versions 5.05-7.55 were preferred).
The PS4 9.00 firmware update includes several notable changes: ps4 9.00 firmware
: Group owners were given the authority to delete groups for all members, and users could leave groups immediately upon blocking another player. This firmware was particularly notable in the modding