Identify this web design software

Factual Questions
1

…unless I just made it up.

A while back I heard about some software that allows you to overlay a Photoshop mockup of a website, presumably with some degree of transparency, over an actual WYSIWYG rendition of the website. You can then adjust CSS on the fly until you get everything aligned the way you intended.

Does this sound familiar to anyone?

2

I think Dreamweaver allows you to do that, at least the one bundled with InDesign CS3.

3

Of course my Google-fu starts working after I post.

It’s a Firefox plugin called Pixel Perfect.