Microsoft’s Outlook Web App help site has the list of web browsers on different OS platforms that support the full Outlook Web App feature set.

To use the complete set of features available in Outlook Web App and the Web management interface, you can use the following browsers on a computer running Windows XP, Windows 2003, Windows Vista, or Windows 7:

• Internet Explorer 7 and later versions.
• Firefox 3.0.1 and later versions.
• Chrome 3.0.195.27 and later versions.

On a computer running Max OS X, you can use:

• Safari 3.1 and later versions.
• Firefox 3.0.1 and later versions.

On a computer running Linux, you can use:

• Firefox 3.0.1 and later versions.

If you use a Web browser that doesn’t support the full feature set, Outlook Web App will open in the light version.

The light version is primarily designed for accessibility for the visually impaired.  However with its stripped down interface and limited features it is also useful when on slow connections and has the broadest browser compatiblity of the two versions.