Right click on the icon you like to use and select show info( or select it and then type opt+i). Select the icon in the top left of the 'show info' window and copy it with the edit menu
1. Right click the Mozilla icon in the dock(or the icon you like to change) and select show in finder.
3. Select the Mozilla application with the mouse. Right click on it an select show info. Then paste the icon over the existin icon.
4. Remove the old icon from the dock by draging out to the desktop. Drag Mozilla now with the new icon into the dock
Comments
1. Right click the Mozilla icon in the dock(or the icon you like to change) and select show in finder.
3. Select the Mozilla application with the mouse. Right click on it an select show info. Then paste the icon over the existin icon.
4. Remove the old icon from the dock by draging out to the desktop. Drag Mozilla now with the new icon into the dock