The worst thing designing a website for someone is the frustration of trying to make every browser render the same. It has become a real challenge to accomplish this task due to the fact that the document object models (DOM)'s are different. Because of the fact that the W3C won't force these corporations to create a standard document object model, things have become very frustrating for a web developer.
The same of course go's for any other browser. If I design things to one browser but then check it for
compatibility in another browser it won't turn out the same. While being able to check webpages for browser compatibility issues, there always has to be some kind of variation from browser to browser, but most issues can be solved with a little extra effort.