I used to think [that you should develop first in IE, then test in Mozilla and the rest], but there’s a good reason why my mindset shifted. If you develop in IE, what happens is that you create dependencies on its buggy rendering.
Since the other browsers don’t use the same flawed rendering, you’ll have to bend over backward to hack your layout into working properly with most of them. In fact, when I was developing in IE, I used to curse Mozilla quite frequently for rendering my code ‘wrong’.
My experience has been that if you start out by developing in Mozilla or Safari, and then test in everything else afterward, you have to do much less hacking to make it work. The fringe browsers benefit; IE5/Mac gets a surprising number of my layouts right without any extra effort. Opera generally cooperates, although it can be a crapshoot at times. IE (per the general tone of this thread) is the big problem.
Can you get away with developing in IE? Of course. Is it easier? Generally not. If you don’t care about the fringe browsers, then you’ll get away with it. If you do care, then you’ll have a far nicer time developing in Mozilla.
Developing for Mozilla (and everything else besides IE) first, and then hacking for IE’s shortcomings has made my Web design life a lot easier. I’m still struggling with a site (can’t give a link yet, sorry), that I designed for IE, and am fervently hacking to get to fit in everything else. It’s a mess. Meanwhile, my sites where I started developing for Mozilla and then hacked for IE are flying high and beautiful.
As I said before you should switch to Mozilla