Just about none of the web designers I know use Internet Explorer as their default browser. But they all have to use it to some extent to make sure that the pages they are design render correctly in IE. It is after all still the most used browser in the world. Switching browsers like this is often a pain. But there's a Firefox add-on that makes this a lot less painful. Once you install it, you can actually see IE rendering of pages directly in Firefox. I have no idea how in the world it works. But it's hot!