This is a known bug in Outlook Web Access. AFAIU it is fixed with service pack 14.1 (see <https://code.google.com/p/chromium/issues/detail?id=41308#c30>).

To clarify the above: you should talk to the administrator of your Outlook Web Access (usually your workplace IT department) and ask that they update. This bug has been fixed in OWA... The broken behavior worked in Firefox 7 and earlier because of an underlying Firefox bug that we've fixed in 8.

Further investigation has shown that Outlook Web Access was only fixed for Chrome (in Exchange 2010 SP1), but not for Firefox (so it's sending different responses to different browsers, and still sends broken content to Firefox).

I encourage people affected to this to open a Support Case at Microsoft while the Firefox team looks into the best way to improve the situation within Firefox.

How do I open a Support Case? I'm having trouble finding the appropriate place on the Microsoft Support website to do this. And does it cost anything?

Firefox 9.0 will revert the 8.0 changes, waiting for a definitive fix from Microsoft: https://bugzilla.mozilla.org/show_bug.cgi?id=703015

Yep, been having this problem about 3 weeks. Finally sent the issue to my IT person, and he sent me here.

One thing I noticed was by forwarding through OWA to my hotmail account I was able to open the attachments w/o a problem from hotmail.

I recommend that your IT person raises a bug report @ Microsoft, too. After all, it's their product which is buggy.

This should now be fixed in Firefox 9 - please download and install it here - mozilla.org/firefox