As of November 2009, Internet Explorer and Firefox are still the browsers of choice as the most common according stats at w3schools.com

Internet Explorer users: 37.7%

Firefox users: 47%

Don’t forget to keep up to date with the latest versions of these browsers. This is free to do. You  can download by clicking the icons above.

Also, Checking your edits to your web site changes in both browsers will ensure your customers see things as you intend them to be.