Try resizing Mozilla 0.9.3 ( Gecko/20010801 ) with the mysql manual loaded (a 2MB HTML file) and it will block the GUI for a considerable amount of time (this is under Windows 2000 on a DUAL CPU machine!). While modifying the layout engine to do a 'lazy', threaded kind of rearranging of the HTML elements like IE does may be a major change, I believe this is a very important feature. (I wonder how KHTML - which is also highly regarded - fares in such a case.)
