Via Scott Hanselman, you can now display a web page with Internet Explorer directly inside a Firefox tab. The extension is called IE Tab, and it provides similar functionality to the older IE View except that it embeds Internet Explorer inside Firefox instead of opening a separate IE window. Once installed, you can right-click a page in Firefox and switch to IE mode without switching tabs. You can also right-click a link and open the link in a new IE tab. You can even configure a list of sites that will always display in an IE tab!
It’s not perfect yet, but 99% of the time it does a fantastic job. Netscape 8.0 has a similar feature, but I find it a bit cumbersome and I really like being able to do it directly in Firefox.