http://imgur.com/a/LbQOc
The image could use a little more contrast, and I would remove the highlight on the bottom of foxkah.  The light source is coming from the top right, so he wouldn't have a highlight on his back unless he was made of gelatin or another transparent material. Another improvement can be made by using the circle tool to create an even curve at the bottom. If you look closely at the logo, it's almost perfectly round with the exception of foxkah's ear.   

Honestly you picked a really hard thing to pixel. The firefox logo is almost all gradients, and I really don't know where to begin with the tail. Sorry I couldn't be of more help.