Client OS version isn't the problem; pretty much any browser, on any OS (including MacOS) should be able to use the basic functionality in the Remote Access web site. Not all browsers will let you use the remote desktop, console/dashboard, or streaming (on
Windows Home Server 2011) but you should be able to at least log in and browse shares.
My suspicion is that there's something wrong with your router configuration. Possibly port 443 hasn't been forwarded to your server? Are you using UPnP? If so, turn it off, assign your server an IP address manually, and forward ports manually.
I'm not on the WHS team, I just post a lot. :)