IE8 and Safari 5 are no longer supported. They should still work but they are not tested regularly and there might be some problems. Like most of the world's Web sites and browser producers, we encourage you to keep your browsers current to improve security and functionality while saving us valuable time.
IE6 and IE7 are not recommended for Moodle 2.6 at all. You will encounter difficulties trying to use those old browsers in today's Internet.