The disable.user.js script just needs to be installed into your particular browser. For Firefox/Greasemonkey simply right click the link and select "Install User Script". With Opera the easiest way is to go into the link and select "Save As" from the "File" menu to save the script into your user script folder. Note that the script is coded so that the dialogs will work when running in a local web server (if you have one) but will be overridden for all sites on the web - if you want to make exceptions you will need to update the include/exclude statements.
This article written by Stephen Chapman, Felgall Pty Ltd.