In those days each browser had their own quirky idea of how to render a website (even Firefox). None of which was really "right" but how IE did it was the de fa

In those days each browser had their own quirky idea of how to render a website (even Firefox). None of which was really "right" but how IE did it was the de facto standard because IE had 90+% marketshare. If you had a site that could potentially be "broken" if the layout didn't render correctly the the easiest thing to do was to test that it worked how you wanted it to in IE and then add a note telling people it might be broken in other browsers (or not serve to them). It wasn't until after people really started focusing on standards compliance and cross-browser compatible frameworks that things got better. The "acid tests" for html/css/js standards compliance helped establish how far along the various browsers were at the time. Most browsers were absolutely terrible in that era, it wasn't until Chrome hit the scene and webkit started taking off that standards compliance started to become a big deal. Eventually most major browsers had decent or good standards compliance in their rendering and things like jQuery helped smooth over the rough spots of differences in browser behavior.