Firefox allows you to impersonate IE. I’m currently running Firefox version 3.5.2.

To get "IE Tabs" you first need to open Firefox. Then, if you go to the “Tools >> Add-ons” section you can do a search for “IE Tab” by clicking the “Get Add-ons” menu option. When you include this add-on you will get a little icon in the lower right corner of the browser. By clicking the little icon you change the browsers engine from IE to Mozilla Firefox.

Firefox in “Mozilla” mode:

Firefox in “IE” mode:

The only visual difference is the little icon in the lower right corner of the browser and the subtle (and at times not-so-subtle) differences in CSS.