As I know, SharePoint has traditionally been designed to work very well on Windows clients, specifically on Internet Explorer in Windows. Much of the rich functionality that SharePoint exposes through IE comes via ActiveX controls, which are supported only in IE on Windows.
Better than other browsers, it is generally suggested that users use Firefox.
<http://www.softsea.com/review/Mozilla-Firefox.html>
There are some known problems when a user is accessing a Sharepoint site from a Mac, such as problem with viewing or editing Office files.