John Frusciante’s Boss FZ-3 Fuzzaccess_time First seen circa 1999
This fuzz pedal was used by John during the early part of the Californication tour, circa 1999 (as seen on his pedalboard during live performances). It was also seen on the photo published by the Guitar Player magazine in September 1999, apparently taken during the studio session. This obviously means that the pedal was possibly used on Californication, although it is unknown on which songs specifically.
However, without any direct quotes from John on the subject, it is also possible that the Boss FZ-3 was used simply for the purpose of reproducing the sound of the BSSM era (during which John likely used a Dunlop Fuzz Face).