I was inspired by the article Make Your Mockup in Markup by Meagan Fisher. I am one of those persons who can’t stand Photoshop and design every bit of a website in it. Also it is not very DRY to design paragraphs, or whatever, in Photoshop and again with CSS.
This is a neat cross-browser alternative to the heavy-duty and Firefox-only Firebug.
To simplify usage of this tool, I made a bookmarklet. It saves you the hassle of including the editor source code in your HTML files manually. Also, I added a close button.
To install, simply drag and drop the link below to your bookmark bar: