After two-weeks of telling the folks at InstantSSL telling me the firewall at work was at fault, and me spending the entire two weeks telling them that my firewall isn’t at fault, they finally got onto the server themselves, and lo-and-behold, they screwed up. But it took them 48 hours to figure out how they screwed up. And it was what I was telling them all along: The root and trusted certs they sent me were screwed up, or the cert they generated for me was generated based on the wrong trust.
Sure enough, it was a combination of all of the above. Regardless, it’s working now, but feel free to tell me if you can’t get to this URL (or check out our office’s Web cam, if you’d like) with it being a trusted, nice, and happy SSL site.