Having been playing around with a CSS layout site for the London .NET user group site re-write I have to say that the Web Developer extension for Firefox is a nice tool when you want to figure out where your id and classes are, where the boxes flow. Very cool.
In fact the whole extensions experience for Firefox seems much better than IE. I am sure there are some good IE add-ins out there – if anyone knows of a good CSS one, please let me know in the comments – but the issue is finding them. Maybe MS needs to encourage an IE plug-in community to develop.
Oh and the CSS renders better in Firefox. Hopefully IE 7.0 will sort some of that out.