Microsoft stopped working on Silverlight over two years ago now and so as web browsers have updated, they no longer work as well with Silverlight as they once did.
I just tried loading a small test synth in Safari, Firefox, and Chrome on an Intel iMac.
Safari didn't fully load the viewer, however both Firefox and Chrome did load and play the synth. If you have Firefox or Chrome on your laptop, I would certainly give them a try. For some reason the viewer does take much longer than normal to load on a Mac, but it will still work.
On a different note, have you taken a look at the Photosynth 2014 Technical Preview? http://photosynth.net/preview
It calculates the photosynths on the website servers instead of requiring you to run the Windows desktop application to make and upload them.
Their new viewer uses WebGL which will work on a Mac in Firefox, Chrome, and Safari (although you'll need to manually enable WebGL in Safari).