One common thing with developing a web page is incompatibility. When you design a web page, you need to make sure that all of the major browsers can view that page correctly. IE, Netscape, Opera, and Fire Fox are the most used browsers. I always views my pages with different browsers to get as compatible with all of these as possible. Don't have a one track mind when it comes to designing pages or you could leave people wanting to view your site in the cold.
IE is one of the most popular browsers, but things can be very different between IE and Fire Fox
I have learned from personal experience that IE can mask bugs that may be hidden in the Mozilla browsers.
Checking you web site on multiple browsers is essential to having a properly functioning web site.