Differend browsers show your website differently. If you want to have your website whown exactly the same on all of the browsers you have to write a valid code. Of course there are some aspects when you dont or even musnt write a valid code to have your website shown nicely on the computer screen, but in most cases you have to write it valid.
I wanted to share you a very great tool for website builders and owners, where you can check how your website looks like on a lot of different browsers. Here you go:
http://browsershots.org/