It would be ideal if HTML and CSS worked the same across all browsers, but that is not the case. Firefox/Mozilla and Internet Explorer (IE) share various computing differences. IE is particularly different in how it computes div width and overflows and max heights. In HotDoodle CSS we allow you to test for the presence of the IE editor and to use alternative CSS to get around its non-standard behavior.
Note: Although many designers prefer Firefox/Mozilla, the biggest market share is still with IE, especially within HotDoodle’s small business target customers. So whenever possible, design for IE 6.0 & IE 7.0 first, and then at least make sure it still is functional and doesn’t completely break in other browsers.