Repeating error: Warning unresponsive script

I get the following error repeatedly when using the calendar function: Hide all calendars or Show all calendars. It's happened more or less from the beginning of V2 for me. Warning: Unresponsive Script
Script: https://ldscdn.org/scripts/jquery/1.5.1 ... .min.js:16

and the feature generally stops at whatever level it was at.
Firefox 11 (but has happened with several previous versions) windows 7