Delete the icon. Find the Directory where Firefox.exe is in and create a short cut and drag to the dock.

There may be a alternative way in properties to change the icon is a Mac so I have no idea. You would know more than I. Everything I looked at is for Windows.

Please let us know if this solved your issue or if need further assistance.

This did work, so thank you. However, usually for Mac, all you do is drag the application icon to the dock and voila. I'm not sure why it needs to be an alias now in order for it to render as the Firefox icon. Thank you for this idea because it did work.