Ok so I know that not only have people asked this before and you have replied Red Panda. But this goes alot deeper than that. the following link shows an article complete with concept art and quotes from your design team. This clearly shows it to be a fox instead of a red panda. read more
To be honest, the Mozilla Firefox animal is officially a fox (Based on the red fox, or Vulpes Vulpes, to be exact). The icon was inspired by a bible story picture book. read more
The logo was revised and updated later, fixing some flaws found when the logo was enlarged. The animal shown in the logo is a stylized fox, although "firefox" is considered to be a common name for the Red Panda. read more