Editing webpages with JavaScript snippet

So, most of you will no doubt know that you can execute JavaScript from the URL bar and how useful it can be. For example, you could view the text is password fields which has proved to be useful on several occassions (alert document.form1.passwordField.text) . An interesting JS snippet I came across was:

javascript:document.body.contentEditable='true'; document.designMode='on'; void 0

Just type that into the URL, then you can start editing the webpage you are viewing straight from the browser.