I'm unable to actually load this, or 3.10 either.

I filed a tech support request and didn't get a call back within the specified time period.
UPDATE: Someone PM'd me to suggest trying the upload using Internet Explorer, as it worked for him after it did not work with Firefox. Guess what? I was able to upload the new firmware! I strongly suggest that D-Link fix this compatibility issue, or at least issue a warning when attempting to upload firmware using any browser not actively tested via their QA process (no comment on the "quality" in their QA).