--- a/toolkit/components/telemetry/TelemetryStorage.jsm
+++ b/toolkit/components/telemetry/TelemetryStorage.jsm
@@ -1803,22 +1803,21 @@ function getPingDirectory() {
 /**
  * Build the path to the archived ping.
  * @param {String} aPingId The ping id.
  * @param {Object} aDate The ping creation date.
  * @param {String} aType The ping type.
  * @return {String} The full path to the archived ping.
  */
 function getArchivedPingPath(aPingId, aDate, aType) {
-  // Helper to pad the month to 2 digits, if needed (e.g. "1" -> "01").
-  let addLeftPadding = value => (value < 10) ? ("0" + value) : value;
   // Get the ping creation date and generate the archive directory to hold it. Note
   // that getMonth returns a 0-based month, so we need to add an offset.
+  let month = new String(aDate.getMonth() + 1);
   let archivedPingDir = OS.Path.join(gPingsArchivePath,
-    aDate.getFullYear() + "-" + addLeftPadding(aDate.getMonth() + 1));
+    aDate.getFullYear() + "-" + month.padStart(2, "0"));
   // Generate the archived ping file path as YYYY-MM/<TIMESTAMP>.UUID.type.json
   let fileName = [aDate.getTime(), aPingId, aType, "json"].join(".");
   return OS.Path.join(archivedPingDir, fileName);
 }
 
 /**
  * Get the size of the ping file on the disk.
  * @return {Integer} The file size, in bytes, of the ping file or 0 on errors.

--- a/toolkit/components/telemetry/TelemetryUtils.jsm
+++ b/toolkit/components/telemetry/TelemetryUtils.jsm
@@ -121,22 +121,18 @@ this.TelemetryUtils = {
 
   /**
    * Date.toISOString() gives us UTC times, this gives us local times in
    * the ISO date format. See http://www.w3.org/TR/NOTE-datetime
    * @param {Object} date The input date.
    * @return {String} The local time ISO string.
    */
   toLocalTimeISOString(date) {
-    function padNumber(number, places) {
-      number = number.toString();
-      while (number.length < places) {
-        number = "0" + number;
-      }
-      return number;
+    function padNumber(number, length) {
+      return number.toString().padStart(length, "0");
     }
 
     let sign = (n) => n >= 0 ? "+" : "-";
     // getTimezoneOffset counter-intuitively returns -60 for UTC+1.
     let tzOffset = -date.getTimezoneOffset();
 
     // YYYY-MM-DDThh:mm:ss.sTZD (eg 1997-07-16T19:20:30.45+01:00)
     return padNumber(date.getFullYear(), 4)