The Council of Florence also declared a few other controversial things - that the souls of the unbaptized would go straight to eternal punishment in hell (this was also understood to include unbaptized infants following the teaching of Bl. Augustine, and the definition of the Council of Carthage of 418 A.D.) The Feeneyites are probably the only ones who still hold this view.
"In the name of the holy Trinity, Father, Son and holy Spirit, we define, with the approval of this holy universal council of Florence....also that the explanationof the words "and from the Son" was licitly and reasonably added to the creed for the sake of declaring the truth and from imminent need....Also, the souls of those who have incurred no stain of sin whatsoever after baptism, as well as souls who after incurring the stain of sin have been cleansed whether in their bodies or outside their bodies, as was stated above, are straightaway received into heaven and clearly behold the triune God as he is, yet one person more perfectly than another according to the difference of their merits. But the souls of those who depart this life in actual mortal sin, or in original sin alone, go down straightaway to hell to be punished, but with unequal pains. "
In contrast, after the Filioque was condemned during the 6th Session of the Council of Constantinople in 879-880 (in the presence of the Papal legates) Pope John VIII made himself clear in his correspondence with St. Photius [Epistle No. 8] that "we preserved it as we originally received it, without adding to or taking anything from it. To set you at ease thus, upon this subject, which has been a cause of scandal to the Church, we again declare to you that not only do we thus recite it but even condemn those who in their folly have had the audacity to act otherwise from the beginning, as violators of the Divine Word, and falsifiers of the doctrine of Christ, of the Apostles, and of the Fathers, who have transmitted the Creed to us through the Councils; we declare that their portion is that of Judas, because they have acted like him, since, if it be not the body of Christ itself which they put to death, it is, at all events, the faithful of God who are his members, whom they tear by schism, giving them up, as well as themselves, to eternal death, as also did that base Apostle. Nevertheless, I think that your Holiness, so full of wisdom, is aware of the difficulty of making our bishops share this opinion, and of changing at once so important a practice which has taken root for so many years. We therefore believe it is best not to force any one to abandon that addition to the Creed, but we must act with moderation and prudence, little by little, exhorting them to renounce that blasphemy. Thus, then, those who accuse us of sharing this opinion do not speak the truth."