I wonder why in the era of CSS Zen and AJAX we aren't able to customize such widely used online applications?
del.icio.us is a good service (I am in the process of writing a big article about social bookmarking services) but the interface is really ugly and often you have to look twice to find something.

Tadeusz, the greasemonkey extension for Firefox does what you ask for:
http://greasemonkey.mozdev.org/

Indeed you're right Roger. Funny thing is, I have Greasemonkey already installed (along 50 other extensions) and used it just for making Flickr photos downloadable...

Maybe I should read what my extensions are about ;-)