A better option is to use Internet Explorer browser version 11.
In any case, you need to add the GPS Explorer url in your Java Control Panel's Exception Site List under the Security tab: http://geoapp03.ucsd.edu/gridsphere/gridsphere?cid=Time+Series+Plots
Mac Users: You can use Chrome, Safari and Firefox 52.2.0 (ESR). Note: There is a problem accessing the Model Terms for MAC users. We are trying to fix this.