For some reason, when I view this page in IE9, all of the @font-face fonts look way smaller than they should, and maybe like a different typeface too. As far as I can tell, everything about my syntax should be cooperating with IE9. Others have had trouble replicating the issue, so maybe it is something in my Windows font settings? Either way, if you want to try to replicate what I am seeing, I am running IE9 on Windows 7 64bit.
EDIT: I'm not sure if this is a problem with the page, or a problem with my browser. Either way, I need to get it fixed.
Looks the same for me in IE9 as other browsers, none are using the embedded font due to its different name (HelveticaMD vs the actual name in use in the CSS, Helvetica.)
It looks like your “wrong” screenshot is of a browser trying to actually use the embedded font, whereas the “right” screenshot is just the default font. If that's what you want, just get rid of the font embedding stuff.