Here is an incomplete list of browsers that are known to work well with Drupal core and support all of its features:
- Internet Explorer 8.x and later (Drupal 7)
- Internet Explorer 9.x and later, read more about it here. (Drupal 8)
- Firefox 5.x and later
- Opera 12 and later
- Safari 5.x and later
- Google Chrome
It is also possible to use a browser that does not support CSS with Drupal, but of course the site will not look very similar to how it looks in a browser that does support CSS.
IE8 and older has a problem with loading more than 31 stylesheets, a situation that may be encountered if you are using a contributed theme or number of contributed modules. An acceptable workaround is to enable CSS aggregation.