This page is used to generate randomized passwords, to whatever security requirements you desire. It works by generating randomized passwords of the desired length, and then checking to see if the random password meets the security requirements. If not, a new one is generated. When a password is generated that meets the desired security, it is displayed in the browser.
It's worth noting that the password is generated by your browser, not by the web server. As such, the web server does not need to be trusted to keep your password secret -- it is never in possession of generated passwords. In fact, generated passwords are never sent over the network at all.
I use this. You should too.