Let’s face it, Internet Explorer and Firefox see pages differently. I normally develop exclusively in Firefox, but the job is never done until the pages look exactly in IE as they appear in Firefox. And you always get frustrated with the browser that you don’t normally work in, which for me would be IE.
I’ve come to appreciate the IE Developers Toolkit in eliminating that frustration. If you use Firefly, then you know all about the Inspect tool, allowing you to hover over a CSS element and determine its properties. In the IE Developers Toolkit, the Select Element by Click function (same far-left location on the add-in toolbar) does the same thing if not better than Firefly. You also learn a lot of browser rendering in the process and eliminate the need for supplemental [if IE] stylesheet directives.