diff --git a/browser/base/content/test/static/head.js b/browser/base/content/test/static/head.js
index 4ac035dabc9a..f2b8204adbd4 100644
--- a/browser/base/content/test/static/head.js
+++ b/browser/base/content/test/static/head.js
@@ -108,11 +108,9 @@ function getURLForFile(file) {
  */
 function* generateEntriesFromJarFile(jarFile, extension) {
   let zr = new ZipReader(jarFile);
-  let entryEnumerator = zr.findEntries("*" + extension + "$");
-
   const kURIStart = getURLForFile(jarFile);
-  while (entryEnumerator.hasMore()) {
-    let entry = entryEnumerator.getNext();
+
+  for (let entry of zr.findEntries("*" + extension + "$")) {
     // Ignore the JS cache which is stored in omni.ja
     if (entry.startsWith("jsloader") || entry.startsWith("jssubloader")) {
       continue;
diff --git a/browser/components/distribution.js b/browser/components/distribution.js
index 00e03c3706f1..c5116170781e 100644
--- a/browser/components/distribution.js
+++ b/browser/components/distribution.js
@@ -94,7 +94,7 @@ DistributionCustomizer.prototype = {
   },
 
   async _parseBookmarksSection(parentGuid, section) {
-    let keys = Array.from(enumerate(this._ini.getKeys(section))).sort();
+    let keys = Array.from(this._ini.getKeys(section)).sort();
     let re = /^item\.(\d+)\.(\w+)\.?(\w*)/;
     let items = {};
     let defaultIndex = -1;
@@ -317,7 +317,7 @@ DistributionCustomizer.prototype = {
     var usedPreferences = [];
 
     if (sections["Preferences-" + this._locale]) {
-      for (let key of enumerate(this._ini.getKeys("Preferences-" + this._locale))) {
+      for (let key of this._ini.getKeys("Preferences-" + this._locale)) {
         try {
           let value = this._ini.getString("Preferences-" + this._locale, key);
           if (value) {
@@ -329,7 +329,7 @@ DistributionCustomizer.prototype = {
     }
 
     if (sections["Preferences-" + this._language]) {
-      for (let key of enumerate(this._ini.getKeys("Preferences-" + this._language))) {
+      for (let key of this._ini.getKeys("Preferences-" + this._language)) {
         if (usedPreferences.indexOf(key) > -1) {
           continue;
         }
@@ -344,7 +344,7 @@ DistributionCustomizer.prototype = {
     }
 
     if (sections.Preferences) {
-      for (let key of enumerate(this._ini.getKeys("Preferences"))) {
+      for (let key of this._ini.getKeys("Preferences")) {
         if (usedPreferences.indexOf(key) > -1) {
           continue;
         }
@@ -369,7 +369,7 @@ DistributionCustomizer.prototype = {
     var usedLocalizablePreferences = [];
 
     if (sections["LocalizablePreferences-" + this._locale]) {
-      for (let key of enumerate(this._ini.getKeys("LocalizablePreferences-" + this._locale))) {
+      for (let key of this._ini.getKeys("LocalizablePreferences-" + this._locale)) {
         try {
           let value = this._ini.getString("LocalizablePreferences-" + this._locale, key);
           if (value) {
@@ -383,7 +383,7 @@ DistributionCustomizer.prototype = {
     }
 
     if (sections["LocalizablePreferences-" + this._language]) {
-      for (let key of enumerate(this._ini.getKeys("LocalizablePreferences-" + this._language))) {
+      for (let key of this._ini.getKeys("LocalizablePreferences-" + this._language)) {
         if (usedLocalizablePreferences.indexOf(key) > -1) {
           continue;
         }
@@ -400,7 +400,7 @@ DistributionCustomizer.prototype = {
     }
 
     if (sections.LocalizablePreferences) {
-      for (let key of enumerate(this._ini.getKeys("LocalizablePreferences"))) {
+      for (let key of this._ini.getKeys("LocalizablePreferences")) {
         if (usedLocalizablePreferences.indexOf(key) > -1) {
           continue;
         }
@@ -461,14 +461,9 @@ function parseValue(value) {
   return value;
 }
 
-function* enumerate(UTF8Enumerator) {
-  while (UTF8Enumerator.hasMore())
-    yield UTF8Enumerator.getNext();
-}
-
 function enumToObject(UTF8Enumerator) {
   let ret = {};
-  for (let i of enumerate(UTF8Enumerator))
+  for (let i of UTF8Enumerator)
     ret[i] = 1;
   return ret;
 }
diff --git a/browser/components/migration/360seProfileMigrator.js b/browser/components/migration/360seProfileMigrator.js
index f8aceef3eea3..e3cecf549e27 100644
--- a/browser/components/migration/360seProfileMigrator.js
+++ b/browser/components/migration/360seProfileMigrator.js
@@ -63,14 +63,10 @@ function parseINIStrings(file) {
                 getService(Ci.nsIINIParserFactory);
   let parser = factory.createINIParser(file);
   let obj = {};
-  let sections = parser.getSections();
-  while (sections.hasMore()) {
-    let section = sections.getNext();
+  for (let section of parser.getSections()) {
     obj[section] = {};
 
-    let keys = parser.getKeys(section);
-    while (keys.hasMore()) {
-      let key = keys.getNext();
+    for (let key of parser.getKeys(section)) {
       obj[section][key] = parser.getString(section, key);
     }
   }
diff --git a/chrome/test/unit/test_bug848297.js b/chrome/test/unit/test_bug848297.js
index 6cab202c13a3..84c694e889a3 100644
--- a/chrome/test/unit/test_bug848297.js
+++ b/chrome/test/unit/test_bug848297.js
@@ -19,12 +19,7 @@ var chromeReg = Cc["@mozilla.org/chrome/chrome-registry;1"]
 chromeReg.checkForNewChrome();
 
 function enum_to_array(strings) {
-  let rv = [];
-  while (strings.hasMore()) {
-    rv.push(strings.getNext());
-  }
-  rv.sort();
-  return rv;
+  return Array.from(strings).sort();
 }
 
 function run_test() {
diff --git a/dom/cache/test/xpcshell/head.js b/dom/cache/test/xpcshell/head.js
index 86306adcf1c3..917a299af1ed 100644
--- a/dom/cache/test/xpcshell/head.js
+++ b/dom/cache/test/xpcshell/head.js
@@ -33,12 +33,7 @@ function create_test_profile(zipFileName) {
                   .createInstance(Ci.nsIZipReader);
   zipReader.open(packageFile);
 
-  var entryNames = [];
-  var entries = zipReader.findEntries(null);
-  while (entries.hasMore()) {
-    var entry = entries.getNext();
-    entryNames.push(entry);
-  }
+  var entryNames = Array.from(zipReader.findEntries(null));
   entryNames.sort();
 
   for (var entryName of entryNames) {
diff --git a/dom/indexedDB/test/unit/xpcshell-head-parent-process.js b/dom/indexedDB/test/unit/xpcshell-head-parent-process.js
index eeaf942731b7..d751d00e6950 100644
--- a/dom/indexedDB/test/unit/xpcshell-head-parent-process.js
+++ b/dom/indexedDB/test/unit/xpcshell-head-parent-process.js
@@ -286,9 +286,7 @@ function installPackagedProfile(packageName)
   zipReader.open(packageFile);
 
   let entryNames = [];
-  let entries = zipReader.findEntries(null);
-  while (entries.hasMore()) {
-    let entry = entries.getNext();
+  for (let entry of zipReader.findEntries(null)) {
     if (entry != "create_db.html") {
       entryNames.push(entry);
     }
diff --git a/dom/quota/test/unit/head.js b/dom/quota/test/unit/head.js
index 6ffc233d8b85..2a0b54b66a51 100644
--- a/dom/quota/test/unit/head.js
+++ b/dom/quota/test/unit/head.js
@@ -171,12 +171,7 @@ function installPackage(packageName)
                   .createInstance(Ci.nsIZipReader);
   zipReader.open(packageFile);
 
-  let entryNames = [];
-  let entries = zipReader.findEntries(null);
-  while (entries.hasMore()) {
-    let entry = entries.getNext();
-    entryNames.push(entry);
-  }
+  let entryNames = Array.from(zipReader.findEntries(null));
   entryNames.sort();
 
   for (let entryName of entryNames) {
diff --git a/js/xpconnect/loader/XPCOMUtils.jsm b/js/xpconnect/loader/XPCOMUtils.jsm
index a09e1b26f03b..07a5051e76d1 100644
--- a/js/xpconnect/loader/XPCOMUtils.jsm
+++ b/js/xpconnect/loader/XPCOMUtils.jsm
@@ -413,10 +413,9 @@ var XPCOMUtils = {
    * @param e The string enumerator (nsIUTF8StringEnumerator or
    *          nsIStringEnumerator) over which to iterate.
    */
-  IterStringEnumerator: function* XPCU_IterStringEnumerator(e)
+  IterStringEnumerator: function XPCU_IterStringEnumerator(e)
   {
-    while (e.hasMore())
-      yield e.getNext();
+    return e;
   },
 
   /**
diff --git a/modules/libjar/test/unit/test_corrupt_1211262.js b/modules/libjar/test/unit/test_corrupt_1211262.js
index f69619c17325..1b71f50f62b0 100644
--- a/modules/libjar/test/unit/test_corrupt_1211262.js
+++ b/modules/libjar/test/unit/test_corrupt_1211262.js
@@ -11,11 +11,8 @@ function run_test() {
                   createInstance(Ci.nsIZipReader);
   zipreader.open(file);
 
-  var entries = zipreader.findEntries('*');
   var failed = false;
-
-  while (entries.hasMore()) {
-    let entryPath = entries.getNext();
+  for (let entryPath of zipreader.findEntries('*')) {
     let entry = zipreader.getEntry(entryPath);
     if (!entry.isDirectory) {
       try {
diff --git a/security/manager/ssl/tests/unit/test_signed_apps.js b/security/manager/ssl/tests/unit/test_signed_apps.js
index 31940dccaaa6..39d12edde94a 100644
--- a/security/manager/ssl/tests/unit/test_signed_apps.js
+++ b/security/manager/ssl/tests/unit/test_signed_apps.js
@@ -25,9 +25,7 @@ function tamper(inFilePath, outFilePath, modifications, newEntries) {
                    .createInstance(Ci.nsIZipReader);
     reader.open(inFilePath);
     try {
-      let entries = reader.findEntries("");
-      while (entries.hasMore()) {
-        let entryName = entries.getNext();
+      for (let entryName of reader.findEntries("")) {
         let inEntry = reader.getEntry(entryName);
         let entryInput = reader.getInputStream(entryName);
         try {
diff --git a/testing/mochitest/chrome-harness.js b/testing/mochitest/chrome-harness.js
index 061cf0f91961..5136413419a3 100644
--- a/testing/mochitest/chrome-harness.js
+++ b/testing/mochitest/chrome-harness.js
@@ -135,9 +135,8 @@ function extractJarToTmp(jar) {
   /* Create dir structure first, no guarantee about ordering of directories and
    * files returned from findEntries.
    */
-  var dirs = zReader.findEntries(filepath + "*/");
-  while (dirs.hasMore()) {
-    var targetDir = buildRelativePath(dirs.getNext(), tmpdir, filepath);
+  for (let dir of zReader.findEntries(filepath + "*/")) {
+    var targetDir = buildRelativePath(dir, tmpdir, filepath);
     // parseInt is used because octal escape sequences cause deprecation warnings
     // in strict mode (which is turned on in debug builds)
     if (!targetDir.exists()) {
@@ -146,9 +145,7 @@ function extractJarToTmp(jar) {
   }
 
   // now do the files
-  var files = zReader.findEntries(filepath + "*");
-  while (files.hasMore()) {
-    var fname = files.getNext();
+  for (var fname of zReader.findEntries(filepath + "*")) {
     if (fname.substr(-1) != "/") {
       var targetFile = buildRelativePath(fname, tmpdir, filepath);
       zReader.extract(fname, targetFile);
diff --git a/toolkit/components/xulstore/tests/xpcshell/test_XULStore.js b/toolkit/components/xulstore/tests/xpcshell/test_XULStore.js
index 8da8dca9fcb7..53174b71d6f4 100644
--- a/toolkit/components/xulstore/tests/xpcshell/test_XULStore.js
+++ b/toolkit/components/xulstore/tests/xpcshell/test_XULStore.js
@@ -26,30 +26,11 @@ function checkValueExists(uri, id, attr, exists) {
 }
 
 function getIDs(uri) {
-  let it = XULStore.getIDsEnumerator(uri);
-  let result = [];
-
-  while (it.hasMore()) {
-    let value = it.getNext();
-    result.push(value);
-  }
-
-  result.sort();
-  return result;
+  return Array.from(XULStore.getIDsEnumerator(uri)).sort();
 }
 
 function getAttributes(uri, id) {
-  let it = XULStore.getAttributeEnumerator(uri, id);
-
-  let result = [];
-
-  while (it.hasMore()) {
-    let value = it.getNext();
-    result.push(value);
-  }
-
-  result.sort();
-  return result;
+  return Array.from(XULStore.getAttributeEnumerator(uri, id)).sort();
 }
 
 function checkArrays(a, b) {
diff --git a/toolkit/content/contentAreaUtils.js b/toolkit/content/contentAreaUtils.js
index 4b28ec530957..e125216742cf 100644
--- a/toolkit/content/contentAreaUtils.js
+++ b/toolkit/content/contentAreaUtils.js
@@ -848,11 +848,8 @@ function appendFiltersForContentType(aFilePicker, aContentType, aFileExtension,
     var mimeInfo = getMIMEInfoForType(aContentType, aFileExtension);
     if (mimeInfo) {
 
-      var extEnumerator = mimeInfo.getFileExtensions();
-
       var extString = "";
-      while (extEnumerator.hasMore()) {
-        var extension = extEnumerator.getNext();
+      for (var extension of mimeInfo.getFileExtensions()) {
         if (extString)
           extString += "; "; // If adding more than one extension,
                                 // separate by semi-colon
diff --git a/toolkit/crashreporter/CrashSubmit.jsm b/toolkit/crashreporter/CrashSubmit.jsm
index b1e6f34481a7..5eef5377bb2a 100644
--- a/toolkit/crashreporter/CrashSubmit.jsm
+++ b/toolkit/crashreporter/CrashSubmit.jsm
@@ -28,9 +28,7 @@ function parseINIStrings(path) {
                 getService(Ci.nsIINIParserFactory);
   let parser = factory.createINIParser(file);
   let obj = {};
-  let en = parser.getKeys("Strings");
-  while (en.hasMore()) {
-    let key = en.getNext();
+  for (let key of parser.getKeys("Strings")) {
     obj[key] = parser.getString("Strings", key);
   }
   return obj;
diff --git a/toolkit/modules/ZipUtils.jsm b/toolkit/modules/ZipUtils.jsm
index 2d64916bea2b..6512d90060ed 100644
--- a/toolkit/modules/ZipUtils.jsm
+++ b/toolkit/modules/ZipUtils.jsm
@@ -105,10 +105,7 @@ var ZipUtils = {
     return (async function() {
       // Get all of the entries in the zip and sort them so we create directories
       // before files
-      let entries = zipReader.findEntries(null);
-      let names = [];
-      while (entries.hasMore())
-        names.push(entries.getNext());
+      let names = Array.from(zipReader.findEntries(null));
       names.sort();
 
       for (let name of names) {
@@ -168,9 +165,7 @@ var ZipUtils = {
 
     try {
       // create directories first
-      let entries = zipReader.findEntries("*/");
-      while (entries.hasMore()) {
-        let entryName = entries.getNext();
+      for (let entryName of zipReader.findEntries("*/")) {
         let target = getTargetFile(aDir, entryName);
         if (!target.exists()) {
           try {
@@ -182,9 +177,7 @@ var ZipUtils = {
         }
       }
 
-      entries = zipReader.findEntries(null);
-      while (entries.hasMore()) {
-        let entryName = entries.getNext();
+      for (let entryName of zipReader.findEntries(null)) {
         let target = getTargetFile(aDir, entryName);
         if (target.exists())
           continue;
diff --git a/toolkit/mozapps/extensions/internal/AddonTestUtils.jsm b/toolkit/mozapps/extensions/internal/AddonTestUtils.jsm
index fb06ab00423a..2b4fd4b3708a 100644
--- a/toolkit/mozapps/extensions/internal/AddonTestUtils.jsm
+++ b/toolkit/mozapps/extensions/internal/AddonTestUtils.jsm
@@ -1172,9 +1172,7 @@ var AddonTestUtils = {
       dir.create(Ci.nsIFile.DIRECTORY_TYPE, FileUtils.PERMS_DIRECTORY);
 
       let zip = ZipReader(xpiFile);
-      let entries = zip.findEntries(null);
-      while (entries.hasMore()) {
-        let entry = entries.getNext();
+      for (let entry of zip.findEntries(null)) {
         let target = dir.clone();
         for (let part of entry.split("/"))
           target.append(part);
diff --git a/toolkit/mozapps/extensions/internal/XPIInstall.jsm b/toolkit/mozapps/extensions/internal/XPIInstall.jsm
index 03d4465c045a..6421550f15c5 100644
--- a/toolkit/mozapps/extensions/internal/XPIInstall.jsm
+++ b/toolkit/mozapps/extensions/internal/XPIInstall.jsm
@@ -339,7 +339,7 @@ XPIPackage = class XPIPackage extends Package {
   }
 
   async iterFiles(callback) {
-    for (let path of XPCOMUtils.IterStringEnumerator(this.zipReader.findEntries("*"))) {
+    for (let path of this.zipReader.findEntries("*")) {
       let entry = this.zipReader.getEntry(path);
       callback({
         path,
diff --git a/toolkit/mozapps/installer/precompile_cache.js b/toolkit/mozapps/installer/precompile_cache.js
index 6f4375284d22..4f11574c6ce3 100644
--- a/toolkit/mozapps/installer/precompile_cache.js
+++ b/toolkit/mozapps/installer/precompile_cache.js
@@ -15,12 +15,7 @@ function endsWith(str, end) {
 }
 
 function jar_entries(jarReader, pattern) {
-  var entries = [];
-  var enumerator = jarReader.findEntries(pattern);
-  while (enumerator.hasMore()) {
-    entries.push(enumerator.getNext());
-  }
-  return entries;
+  return Array.from(jarReader.findEntries(pattern));
 }
 
 function dir_entries(baseDir, subpath, ext) {
diff --git a/uriloader/exthandler/HandlerService.js b/uriloader/exthandler/HandlerService.js
index d786b9c96150..aea2abfed2aa 100644
--- a/uriloader/exthandler/HandlerService.js
+++ b/uriloader/exthandler/HandlerService.js
@@ -277,10 +277,9 @@ HandlerService.prototype = {
     }
 
     if (this._isMIMEInfo(handlerInfo)) {
-      let extEnumerator = handlerInfo.getFileExtensions();
       let extensions = storedHandlerInfo.extensions || [];
-      while (extEnumerator.hasMore()) {
-        let extension = extEnumerator.getNext().toLowerCase();
+      for (let extension of handlerInfo.getFileExtensions()) {
+        extension = extension.toLowerCase();
         // If the caller stored duplicate extensions, we save them only once.
         if (!extensions.includes(extension)) {
           extensions.push(extension);
diff --git a/xpcom/tests/unit/test_iniParser.js b/xpcom/tests/unit/test_iniParser.js
index 14dde5666d49..21053ffae487 100644
--- a/xpcom/tests/unit/test_iniParser.js
+++ b/xpcom/tests/unit/test_iniParser.js
@@ -44,17 +44,11 @@ function checkParserOutput(parser, expected) {
 function getParserOutput(parser) {
     let output = {};
 
-    let sections = parser.getSections();
-    Assert.ok(!!sections);
-    while (sections.hasMore()) {
-        let section = sections.getNext();
+    for (let section of parser.getSections()) {
         Assert.equal(false, section in output); // catch dupes
         output[section] = {};
 
-        let keys = parser.getKeys(section);
-        Assert.ok(!!keys);
-        while (keys.hasMore()) {
-            let key = keys.getNext();
+        for (let key of parser.getKeys(section)) {
             Assert.equal(false, key in output[section]); // catch dupes
             let value = parser.getString(section, key);
             output[section][key] = value;