[Mediawiki-l] making extra buttons in edit page tool

[Rein]

Okay!
Made the Mediawiki:editpage.js.

If I understand the js correctly there are three extra buttons made allready.
For instance:
addInsertButton('wikipedia/commons/1/11/Button_category.png','Category','[[Category:',']]','');
It's clear that the address is not correct.
I put a button in skins/common/images
and changed the address..... 
but nothing happens.
I tried a complete url, a relative url ... but no success.
What am I doing wrong?