I mainly remember 1) IE being quite idiosyncratic in how it followed html/css standards and 2) being able to use things like firebug to debug FF, but having an alert window pop up with a cryptic, unhelpful message when trying to debug IE. It seemed "make it work in IE6" was like 30% of time spent in my work back then. Also, it stuck around for a _long_ time, so that was especially annoying as long after other browsers, including IE, had moved on, a lot of effort still went into supporting IE6.