A bishop from Caesarea named Firmilian sided with Cyprian in his dispute, seething against Stephen's "insulting arrogance" and claims of authority based on the See of Peter.
His great successor in Cappadocia, St Basil of Caesarea, mentions his view on heretical baptism without accepting it (Epistle clxxxviii), and says, when speaking of the expression "with the Holy Ghost" in the Doxology: "That our own Firmilian held this faith is testified by the lógoi which he has left" (De Spiritu Sancto, xxix, 74).
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Gregory of Nyssa tells that Gregory Thaumaturgus, when still a pagan, having completed his secular studies, "fell in with Firmilian, a Cappadocian of noble family, similar to himself in character and talent, as he showed in his subsequent life when he adorned the Church of Caesarea."
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The letter of the third council says he was too easily persuaded that Paul of Samosata would amend; hence the necessity of another council (Eusebius, VII, iii-v).
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Firmilian also took part in the first of two councils at Antioch which discussed deposing Paul of Samosata, in 266 (Wace).
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Later, when bishop, Eusebius records (Ecclesiastical History, VI, xxvi-xxviii), he invited Origen to his own country, at the time (232–35) when the great teacher was staying in Caesarea of Palestine.
At Caesarea, Origen was joyfully received, was the guest of Firmilian, bishop of Caesarea in Cappadocia, and perhaps also of the empress-dowager Julia Avita Mamaea.
Firmilian tells of a woman who went into an ecstasy and came out a prophetess.