… It is called Webolodeon:
The original hack was a witch’s brew of PHP and a Perl http proxy. I’ve hacked the basic idea into a script for plugin-de-jour GreaseMonkey. Your last unconfined act of browsing, then is to the user script page, where you should be able to install it using Tools->Install User Script. (This is all Firefox-only, natch).
Once installed, you will be pestered every 5 minutes to make a case for your further web browsing. If your work is done, just cancel the dialog box and quit the app; if you’re not finished (and you really need to keep zipping around the Interweb a bit longer), insert a virtual nickel by typing a summary of what you’re working on. This buys you another five minutes. And so on. The script resets the timer after three minutes, so if you spend more than that staring at one page, you’ll have beaten the system. I didn’t tell you that.
New Greasemonkey is keep coming and coming. Life is good. This is going into my Greasemonkey post’s top recommendation list as well. :)
Download Webolodeon Greasemonkey script – [Oblomovka]