Websites built using just Drupal core are compatible with, and fully functional, in all modern browsers that support CSS and JavaScript. However, browsers have varying levels of compliance with Internet standards such as CSS 2, so there may be minor variations in appearance.
Here is an incomplete list of browsers that are known to work well with Drupal core and support all of its features:
Internet Explorer 6.x and later
Firefox 2.x and later
Opera 7 and later
Safari 1.x and later
Camino 1.x and later
Google Chrome
It’s worth mentioning here that IE6 has an problem with loading more than 30 stylesheets, and it’s fairly easy to run into this problem once you start adding contrib modules.
PHP Recommended: PHP 5.2.x
Required: PHP version 4.3.5 or higher.