Firefox has all the plugins you can poke a stick at, but what to do when IE is doing its “thing”? Windows Explorer plugins to the rescue!
Microsoft has their own IE Developer Toolbar that is similar to the Firefox Firebug plugin. It lets you inspect and alter the DOM, change settings, outline elements, find CSS etc.
That should make the bughunt slightly easier for everyone.
Update: I’m running multiple IE’s, and as a result (I assume) the webtools only work in IE7.