A frustrating thing about designing and developing websites is that sometimes they look different on different computers. Some variables to consider when thinking about why they look different are the visitor’s operating system, the visitor’s display resolution and the visitor’s web browser. Usually operating systems don’t play a huge role in how a website visually appears unless it’s a handheld device, and as long as your site isn’t wider than 1024 pixels, you shouldn’t have to worry much about the resolution issue. Web browsers however are usually the main reason why websites can look different. You can try to download all the latest web browsers and load your site separately on them but what about the older versions of browsers that you can’t install anymore? Those treat your code different as well.
The solution that I found helps with the browser issue is working with a fantastic website called Browsershots. Browsershots will simply let you type in the URL of the website that you want to check and then give you a series of screenshots with the results of how it would look in different browsers. Browsershots covers all of the basic browsers (Firefox, Internet Explorer, Safari & Chrome) and also shows examples of sites in some of the more obscure web browsers (Dillo, Iceape, Minefield & Avant). After using Browsersshots, I go in and tweak the code until it looks correct across browsers and then check it again. Browsershots is free to use.
More @ Browsershots.