How to change mozilla progresbar?

[Kjartan]

Haow I can change this progressbar?

Where I can find progressbar on this image:
http://zapodaj.net/7aa6a7bb06ed.png.html

[Mr GRiM]

Buttons, Boxes & Controls > Progress Bars > Normal > Chunk
Buttons, Boxes & Controls > Progress Bars > Normal > Fill