Rebranding an existing site is always process, especially if site must maintain same page structure and, in case of MOSS WCM site, all web parts and content controls must stay alive and in place, so to speek. If you're changing colors and positioning of elements and layout must stay the same in Firefox, IE 6, IE 7, Opera... (and Safari etc...) there's no need to explain old facts again - they all don't render pages in same way. Problems can arise in a pixel or two, or ten... or more... :) and one tool that can save the day is Firebug. I especially like to use its css window, disable some style attributes and to watch its impact on layout of that element. Another feature that I like is Layout tab where you can see complete box model of an element.
More screenshots can be seen on its official page http://www.getfirebug.com/Cross Posted from http://sharepointblogs.com/panjkov/