The X-Ray Firefox Extension

Today I found what may be the second best Firefox extension I have ever seen (the first being the almost-impossible-to-beat Web Developer's Toolbar from Chris Pederick). The X-Ray Firefox Extension (from Stuart Robertson) shows you which tags are being used by different elements on a webpage, all without having to sort through the sourcecode. It's a great way to troubleshoot a design, or reverse-engineer something you might see on another site.

If you do any kind of web design, it's a must. Download it now.