Is it though? To me the animal on logos used by Firefox [1] always looked more similar to a red fox [2] than a red panda. Note pointy nose with the bottom colored white. Even the latest logo that shows more of the side of the face lacks the kind of patterns distinctive of the red panda. The -fire part of the name seemed to be represented by the flaming tail, not the animal itself.
Yes, especially the first Firefox logo has a distinct snout. I have no primary source to quote, but there are plenty claims, referencing each other, that the name stems from the nickname of the red panda.
I was wondering if there is any official statement about the name.
But it seems most common to think of a (speedy?) fox with a flaming tail. How to derive a dog's burning relative from a phoenix seems to remain uncertain.
[1] https://logos-world.net/wp-content/uploads/2021/08/Firefox-L...
[2] https://en.wikipedia.org/wiki/Red_fox