It only works in Firefox, and you’ll need to install a program called Greasemonkey (also linked to on the above page) before you can use it. But once you do, it’s a nifty little program.
And you know it works, because if it hadn’t, I would have been able to post this to lj a couple hours ago instead of waiting until now. 🙂
Now, to see for how long I have the discipline to keep the program installed …