--- a/toolkit/content/aboutTelemetry.js
+++ b/toolkit/content/aboutTelemetry.js
@@ -170,17 +170,17 @@ function removeAllChildNodes(node) {
     node.removeChild(node.lastChild);
   }
 }
 
 /**
  * Pad a number to two digits with leading "0".
  */
 function padToTwoDigits(n) {
-  return (n > 9) ? n : "0" + n;
+  return new String(n).padStart(2, "0");
 }
 
 /**
  * Return yesterdays date with the same time.
  */
 function yesterday(date) {
   let d = new Date(date);
   d.setDate(d.getDate() - 1);