So, you’re a web developer, and you’ve been using the Web Developer toolbar along with the DOM Inspector in Firefox, and wishing that such a thing was available for Internet Explorer? (Well, there were such things available, but they’re from third parties, and they cost money, and now…) You’re in luck!
Microsoft just released the Internet Explorer Developer Toolbar Beta which provides several features for deeply exploring and understanding Web pages as rendered in IE.
You should deffinitely check this out if you design web-pages, it’s pretty handy. Oh, and if you’ve never played with Fiddler (it’s browser independent), it’s a really cool tool for HTTP debugging (notice I said HTTP, not HTML). It (temporarily) serves as a proxy for all your web traffic, so you can not only see all requests as they go out, you can set breakpoints, and even tweak requests so you can see in IE the results of identifying as Firefox, or vice-versa. There’s a good tutorial for using Fiddler in the MSDN