When you’re building a site, make sure you check out your site in multiple web browsers other than the one you use regularly.
The ones you want to pay attention to (other than Internet Explorer and Firefox) are Chrome, Safari, and Opera.
If you’re on a Mac, unless you have a virtualized Windows installation, then IE is easily not available. So a great way to QA your site is with Adobe’s Browser Labs web app that will let you see how different web browsers render your site. They also have multiple versions of IE available. Sometimes the different versions of Internet Explorer renders pages very different from each other. Adobe Browser Labs is free and easy to use.
Remember that your site’s not going to always look perfect in all the browsers so if you’re 95% “good to go” with most of the browsers especially if it’s IE and Firefox, then launch your site and make post launch fixes.
Get it: Adobe’s Browser Labs