The Firefox plugin to use now is DNS Flusher.
This Quix Bookmarklet might not work like intended. If you change DNS for a website, and want to know if you see the old or new one, this won't work reliably. It does not get the host info for your computer, but that for the Quix webserver. They may be different.
When you use this bookmarklet, it probably never has visited your website, so the host info it gets is the latest, totally fresh. Your laptop still might use the old cached info.
If you change your local hosts file, it will never work. DNS Flusher will work in this case.
So if you just want to know the IP of a certain website, no problem, Quix will do its job. If this is about changing DNS info, don't rely on it, use Firefox with DNS Flusher, or use a Terminal (available for iOS and Android as well).