--- a/browser/modules/Sanitizer.jsm
+++ b/browser/modules/Sanitizer.jsm
@@ -201,16 +201,17 @@ var Sanitizer = {
       case Sanitizer.TIMESPAN_4HOURS :
         startDate = endDate - 14400000000; // 4*60*60*1000000
         break;
       case Sanitizer.TIMESPAN_TODAY :
         var d = new Date(); // Start with today
         d.setHours(0); // zero us back to midnight...
         d.setMinutes(0);
         d.setSeconds(0);
+        d.setMilliseconds(0);
         startDate = d.valueOf() * 1000; // convert to epoch usec
         break;
       case Sanitizer.TIMESPAN_24HOURS :
         startDate = endDate - 86400000000; // 24*60*60*1000000
         break;
       default:
         throw "Invalid time span for clear private data: " + ts;
     }