The good news is a few weeks ago they announced full support of all features in some other browsers, so once the update is available and installed (it should be available late this year or early next year) and installed most any browser will give you full features.

If it helps, this is the difference:

There are two versions of OWA: the rich version and the reach version. The version that you use depends on the web browser that you use to access OWA. If you use Microsoft Internet Explorer 5.0 for Windows or later, you receive the rich version. If you use Internet Explorer 4.02 or earlier, or any other standard web browser on a PC, Mac, or Unix based computer, you receive the reach version.

The rich version supports proprietary "rich" features, such as dynamic HTML (DHTML), the Web Distributed Authoring and Versioning (WebDAV) protocol, XML, and Extensible Stylesheet Language (XSL). Internet Explorer 5.0 and later are considered "rich" browsers.

The reach version does not support these extended feature sets but does support basic capabilities, such as HTML 3.2 and European Computer Manufacturers Association (ECMA) script standards. Internet Explorer 4.02 and earlier versions of Internet Explorer, as well as Firefox and Netscape Navigator, are considered reach browsers.

The reach version uses a simpler user interface than the rich version because it was designed for browsers that do not have proprietary DHTML and XML support.

Some of the extended features available in the rich version of Outlook Web Access (Internet Explorer 5.0 for Windows and higher) include:

Advanced view options, such as the preview pane and sorting
New mail notification
Search
Calendar reminders
Advanced calendar controls and printing
Public folders
Drag-and-drop editing
Tree control