One of the best features in the newest version of Expression Web is Super Preview. Super Preview allows you to view your web pages in different browsers at different resolutions. The point is to 'debug', or fix, your web pages so that they appear nearly the same across all browsers.
Don't let the word, 'debug', throw you for a loop. Debugging is nothing more than 'fixing the bugs' or just making things look right. Nothing more.
Take a look at this YouTube video that I created a few days ago. I think you will learn a bit more than how Super Preview works. You might also learn something about default margins and padding that web browsers apply to our web pages, and how differently they do so.