Always wanted to draw some kind of giant animal screaming/screeching/roaring at Celestia. I think it's a thing. Also, the bird ain't on fire, forgot about that....well they don't literally need to be on fire to be a firebird right? All phoenixes are firebirds but not all firebirds are phoenixes.
Anyways, according to my head-canon, this happens before harmony/search for (the elements of) harmony. On another note, I really do love Fantasia 2000's Firebird Suite sequence.
Celestia, of course, rightfully belongs to
Edit: AHA! I knew I was forgetting something! I forgot to put celestia's wings! Be right back!
Edit 2: And back with wings!