Hey Bird, just wanted to let you know that I'm enjoying Swifthawk's comic a ton! Is it okay if I add my own thoughts as to why Firestar snapping at Swifthawk might have taken people by surprise? (Though, yeah, Swift really deserved it that time). I think if you look at the Darkest Hour with Darkstripe poisoning Sorrelkit and his trail and exile, Firestar was pretty cool, took time to question Darkstripe's side, and was even thought he wanted to give Darkstripe a fair trial so not even Tigerstar's allies could accuse him of favoritism despite, you know, attempted murder being the crime. So I think it surprises people that Firestar's calm and collected in an attempted murder trial and snaps at one of his warriors trying to goad him. In fact, I don't think it's until Sunset when the Clan is arguing against allowing Stormfur and Brook to stay that Firestar snaps that his mind is made up, and it's treated as being very shocking and out of character for Firestar. Though I hope you don't take that in a negative way, as it's made very clear that Firestar's upset by what he just had to say and do, so I don't think it makes him unlikable or unsympathetic. And I am excited to see how Swifthawk and Firestar can eventually reconcile though (as you said he does find his way home again)! Keep up the great work!
As I was reading this analysis, I really tried to ask myself why Firestar's response felt accurate and even inevitable, and I think I found it.
Firestar trusts Swifthawk.
Swift wasn't just another Darkstripe that Fire could never relax around. While they haven't always agreed, they maintained respect for one another as clanmates. While Swift's escalating anger was concerning, Fire still had no doubts about his loyalty to both himself and ThunderClan. So to hear Swift echoing his father's opinion was a stab in the back. It invalidates every encounter up til now, where Swift showed some respect for Fire, proving he never stopped seeing him as a kittypet and little more.
(I actually tried to foreshadow this a few times, particularly when he asks Bramblepaw, "What's it like training under a kittypet?" Despite everything Firestar has done to try to help him, Swift struggles to see past his origins.)