This particular dumb bastard still uses Microsoft because someting like 97% of my customers still do too... I need to be seeing what they are seeing, as they are seeing it. Firefox is OK (I have it here and even use it occasionally) but I don't like the way it displays some things and I don't have the time to spend trying to figure out another piece of software and customise it to do what IE already does -out of the box.
If you use standard HTML, then all broswers should show the pages correctly.
IE is terrible, with its proprietry coding and bloat in general.
www.opera.com user for years here, wouldn't think of using anything else. Years ahead of IE in pretty much every way.