dock icon question?

I downloaded a fire fox icon that's blue and black to go with the rest of my dock icons. The only problem is that the icon in the top right corner when you go to "get info" is not the ff icon, but another like place holder icon. Is it because it's a .png file? How do i fix it or where can I get another black and blue ff icon? Thankss.

I think you need an icns file. Here you go this should work:
Carbon Firefox by ~Leo6247 on deviantART

worked perfect. thank you very much. i'm new at this stuff.