Since the link in the tutorial for ChromEdit Firefox 1.5+ is broken, I have uploaded the file to Rapidshare
http://rapidshare.de/files/33480437/chromeditplusSE-2.5.6.xpi.html
Download it, and on Firefox go to File -> Open, open chromeditplusSE-2.5.6.xpi, and it will be installed, just follow the tuto`s instructions then