I don't seem to be able to edit the original post, so just to clarify my situation: I am working on a Windows Server 2012 box which does not have MBAE installed. Because company policy prohibits browsing from servers, I use Remote Desktop to connect to a Windows 7 box which has Firefox and MBAE installed. When I do so, Firefox will not open unless I disable MBAE. This issue does not affect any other browser or program. When I logon at the Windows 7 box itself (i.e. not via RDP), Firefox will start whether regardless of whether or not MBAE is enabled.