The FOPE team has created a table that shows our browser support matrix. This table below shows the browser and operating system matrix and our tier levels for support. The Tier levels are defined in the Support Level table below.
Forefront Online Protection for Exchange  Admin Center & Message Quarantine Browser support Matrix.
Browser / OS
Windows XP
Windows Server 2003
Windows Vista
Windows 7
Windows Server 2008
IE 6.x
Tier3
Tier3
 
 
 
IE 7.x
Tier2
Tier2
Tier1
 
 
IE 8.x
Tier2
Tier2
Tier1
Tier1
Tier2
Firefox 3.5+
Tier2
Tier2
Tier1
Tier1
Tier2
Everything Else
Tier3
Tier3
Tier3
Tier3
Tier3

Forefront Online Protection for Exchange Browser Support Level Definitions
Support Level
Definition
TIER 1
All advanced features should work well, full testing is done, and bugs fixed/triaged at par with any other feature. All bugs will be triaged and fixed.  There may be some cases where certain functionality (e.g. ActiveX controls) is only available only via a specific browser.
TIER 2
Tier2 support means all functionality should be accessible, but only a sanity test is required and we will rely on inherent compatibility offered by the browser.  However major bugs will be triaged and fixed.
TIER 3
Tier3 implies no support at all.  This tier encompasses all other browsers not listed in the current matrix.