IE Tab - an extension from Taiwan, features: Embedding Internet Explorer in tabs of Mozilla/Firefox...

This is a great tool for web developers, since you can easily see how your web page displayed in IE with just one click and then switch back to Firefox.

If you need some instructions.
Please visit our official website on http://ietab.mozdev.org

Works with:
Firefox: 1.5 – 3.0a5

Download IE Tab
It's free and installs in seconds