"Andrew
This sounds like a Java problem. Although the fact that double click isn't working is troubling. I will investigate this.
In the next update of the viewer you should be able to zoom with the + and - keys.
Yeah I guess it is. It worked fine in the previous java version across all browsers.
God I hate Java 7 on OS X...
Having the + and - as zoom should fix or at least work-around the issue, as the keyboard shortcuts still work.