IE 6, IE 7 and Firefox are currently the mostly-used browsers. They account for more than 85% of all browsers used. You can find the browsers’ monthly report here.
If your theme work on Firefox but look terrible on IE 6 and 7, you will be losing more than 40% of visitors. That’s why it is important to have a theme tested on all 3 browsers.
And it is not easy to have a theme work perfectly on these browsers. Our theme checkers will load the theme on IE 6, IE 7 and Firefox. If abnormality found in any one of the 3 browsers, the theme fails the test.
Themes that pass IE 6 and IE 7 will be awarded 1 point each. Themes that pass Firefox will be awarded 2 points.