The co-writer of the song "Firework" also wrote which song by singer Chris Brown?
Firework (song):  Perry co-wrote the song with Ester Dean and its producers StarGate and Sandy Vee. Ester Dean: Esther Renay Dean (born April 15, 1982), known professionally as Ester Dean, is an American singer, songwriter, record producer, and actress. Ester Dean:  Her 2009 single "Drop It Low" featured singer Chris Brown.
"Drop It Low"