When I found out CheckBoxMate wasn't going to work with Firefox 3.6.3, I was not pleased. I even tried a couple of hacked versions I found floating around the web. None of them worked correctly, so I decided to port this bad boy to Greasemonkey. Now it works beautifully (so far).
Explanation here: http://macdougalmedia.com/2010/04/07/checkboxmate-for-greasemonkey/
Install here: http://userscripts.org/scripts/show/73700
If you aren't familiar with Greasemonkey, it's another amazing add-on for Firefox and you can read more about it here: https://addons.mozilla.org/en-US/firefox/addon/748.