You can never tell who might type your url into their browser. You also don’t know which browser they might be using or which version of that browser they might be using. All browsers may not render your site as you expect it to be seen or even want it to be seen. Viewing your site in more than one browser is an important part of website design.
The current article on Smashing Magazine’s blog Browser Tests, Services and Compatibility Test Suites says the following:
“Cross-browser compatibility is still one of the most complex issues when it comes to web-development. Web standards usually guarantee a (relatively) high degree of consistency, however no browser is perfect and particularly older browsers have always been quite good at surprising web-developers with their creative understanding of (X)HTML/CSS-code. Still you need to make sure that (at least) most visitors of your web-site can use it, navigate through it and find what they’re looking for as quickly as possible.
Firefox on Linux doesn’t display web-sites as Firefox on Windows does. As bonus web-developers have to cope with dozens of versions and, of course, Internet Explorer 6 — 46% of browser usage share, which is a true godsend for hardcoders and hackers. It’s almost impossible to keep all possible problems in mind — a detailed test helps you to identify the critical issues — also and particularly if these are the smallest details of your layout.”
Do you know what your site looks like in anything other than the default browser you have installed on your computer?