--- a/toolkit/content/aboutTelemetry.js
+++ b/toolkit/content/aboutTelemetry.js
@@ -56,22 +56,18 @@ var documentRTLMode = "";
  * Caches result of check on first invocation.
  */
 function isRTL() {
   if (!documentRTLMode)
     documentRTLMode = window.getComputedStyle(document.body).direction;
   return (documentRTLMode == "rtl");
 }
 
-function isArray(arg) {
-  return Object.prototype.toString.call(arg) === "[object Array]";
-}
-
 function isFlatArray(obj) {
-  if (!isArray(obj)) {
+  if (!Array.isArray(obj)) {
     return false;
   }
   return !obj.some(e => typeof(e) == "object");
 }
 
 /**
  * This is a helper function for explodeObject.
  */
@@ -79,17 +75,17 @@ function flattenObject(obj, map, path, a
   for (let k of Object.keys(obj)) {
     let newPath = [...path, array ? "[" + k + "]" : k];
     let v = obj[k];
     if (!v || (typeof(v) != "object")) {
       map.set(newPath.join("."), v);
     } else if (isFlatArray(v)) {
       map.set(newPath.join("."), "[" + v.join(", ") + "]");
     } else {
-      flattenObject(v, map, newPath, isArray(v));
+      flattenObject(v, map, newPath, Array.isArray(v));
     }
   }
 }
 
 /**
  * This turns a JSON object into a "flat" stringified form.
  *
  * For an object like {a: "1", b: {c: "2", d: "3"}} it returns a Map of the