To make sure your website looks great and works all the time, no matter who’s looking at it from where, we Web designers have to do a lot of testing.
All browsers handle or “parse” HTML and CSS differently, and that also includes the different versions of the browsers. We physically view the sites on the different browsers during Web builds to see if everything is displaying and working correctly. For the most part Firefox, Safari and Chrome are very comparable in the way they handle code and display and are really the best choice for end users in general. Internet Explorer, however, is the beast of burden in the Web design industry and, unfortunately, is the most widely used.
The biggest problems is Internet explorer version 6 and earlier. Its inability to display pngs is one of the major issues and although there are fixes, it is a pain. Furthermore, these Internet Explorer versions don’t understand a lot of the CSS properties that are used today or that can be used. So the simple question is why doesn’t everyone just upgrade, well most home users have indeed upgraded without even knowing it, and anyone who has purchased a computer lately will have the new versions of IE. The drawback is that a lot of corporations have not upgraded due to application compatibility issues. Even still, IE is just a rotten apple, a rotten apple that some designers (not us) refuse to even optimize for.
Homework! Test your own website on Safari, Firefox, Internet Explorer and Google Chrome and see for your self!