If you love Firefox but still find there are some sites that annoyingly only work with IE, there is help in the form of an extension for Firefox that provides a tab that hosts the IE engine to render some pages in IE but within Firefox.
Okay, it relies on IE (so this is Windows only also), and isn’t as good as the web site designer actually supporting Firefox, but there are some who will never change or perhaps use Windows specific ActiveX controls that will only work on IE, so handy until people change their ways and means you don’t have to leave your favourite browser.
More info and download of the extension here: