At the moment, I cannot recall which other browsers use WebKit, too, but if Firefox doesn't use it yet, I suspect that Firefox 4 will.
In my experience, there are far too many websites that do not work well (or completely) with anything but versions of Internet Explorer. Microsoft encourages "customization" for I.E. because they are still convinced that they must, even if they can't, seize control of the Internet with their web browser.
Keep Up with TechRepublic