diff --git a/browser/base/content/browser.js b/browser/base/content/browser.js
index 045f2110872..95ac122a11c 100644
--- a/browser/base/content/browser.js
+++ b/browser/base/content/browser.js
@@ -5099,28 +5099,16 @@ function charsetLoadListener (event)
 }
 
 /* Begin Page Style Functions */
-function getStyleSheetArray(frame)
-{
-  var styleSheets = frame.document.styleSheets;
-  var styleSheetsArray = new Array(styleSheets.length);
-  for (var i = 0; i < styleSheets.length; i++) {
-    styleSheetsArray[i] = styleSheets[i];
-  }
-  return styleSheetsArray;
-}
-
-function getAllStyleSheets(frameset)
-{
-  var styleSheetsArray = getStyleSheetArray(frameset);
-  for (var i = 0; i < frameset.frames.length; i++) {
-    var frameSheets = getAllStyleSheets(frameset.frames[i]);
+function getAllStyleSheets(frameset) {
+  var styleSheetsArray = Array.slice(frameset.document.styleSheets);
+  for (let i = 0; i < frameset.frames.length; i++) {
+    let frameSheets = getAllStyleSheets(frameset.frames[i]);
     styleSheetsArray = styleSheetsArray.concat(frameSheets);
   }
   return styleSheetsArray;
 }
 
-function stylesheetFillPopup(menuPopup)
-{
+function stylesheetFillPopup(menuPopup) {
   var noStyle = menuPopup.firstChild;
   var persistentOnly = noStyle.nextSibling;
   var sep = persistentOnly.nextSibling;
@@ -5128,41 +5116,42 @@ function stylesheetFillPopup(menuPopup)
     menuPopup.removeChild(sep.nextSibling);
 
   var styleSheets = getAllStyleSheets(window.content);
-  var currentStyleSheets = [];
+  var currentStyleSheets = {};
   var styleDisabled = getMarkupDocumentViewer().authorStyleDisabled;
   var haveAltSheets = false;
   var altStyleSelected = false;
 
-  for (var i = 0; i < styleSheets.length; ++i) {
-    var currentStyleSheet = styleSheets[i];
+  for (let i = 0; i < styleSheets.length; ++i) {
+    let currentStyleSheet = styleSheets[i];
+
+    if (!currentStyleSheet.title)
+      continue;
 
     // Skip any stylesheets that don't match the screen media type.
-    var media = currentStyleSheet.media.mediaText.toLowerCase();
-    if (media && (media.indexOf("screen") == -1) && (media.indexOf("all") == -1))
+    let (media = currentStyleSheet.media.mediaText.toLowerCase()) {
+      if (media && (media.indexOf("screen") == -1) && (media.indexOf("all") == -1))
         continue;
+    }
 
-    if (currentStyleSheet.title) {
-      if (!currentStyleSheet.disabled)
-        altStyleSelected = true;
+    if (!currentStyleSheet.disabled)
+      altStyleSelected = true;
 
-      haveAltSheets = true;
+    haveAltSheets = true;
 
-      var lastWithSameTitle = null;
-      if (currentStyleSheet.title in currentStyleSheets)
-        lastWithSameTitle = currentStyleSheets[currentStyleSheet.title];
+    let lastWithSameTitle = null;
+    if (currentStyleSheet.title in currentStyleSheets)
+      lastWithSameTitle = currentStyleSheets[currentStyleSheet.title];
 
-      if (!lastWithSameTitle) {
-        var menuItem = document.createElement("menuitem");
-        menuItem.setAttribute("type", "radio");
-        menuItem.setAttribute("label", currentStyleSheet.title);
-        menuItem.setAttribute("data", currentStyleSheet.title);
-        menuItem.setAttribute("checked", !currentStyleSheet.disabled && !styleDisabled);
-        menuPopup.appendChild(menuItem);
-        currentStyleSheets[currentStyleSheet.title] = menuItem;
-      } else {
-        if (currentStyleSheet.disabled)
-          lastWithSameTitle.removeAttribute("checked");
-      }
+    if (!lastWithSameTitle) {
+      let menuItem = document.createElement("menuitem");
+      menuItem.setAttribute("type", "radio");
+      menuItem.setAttribute("label", currentStyleSheet.title);
+      menuItem.setAttribute("data", currentStyleSheet.title);
+      menuItem.setAttribute("checked", !currentStyleSheet.disabled && !styleDisabled);
+      menuPopup.appendChild(menuItem);
+      currentStyleSheets[currentStyleSheet.title] = menuItem;
+    } else if (currentStyleSheet.disabled) {
+      lastWithSameTitle.removeAttribute("checked");
     }
   }
 
@@ -5174,20 +5163,15 @@ function stylesheetFillPopup(menuPopup)
 }
 
 function stylesheetInFrame(frame, title) {
-  var docStyleSheets = frame.document.styleSheets;
-
-  for (var i = 0; i < docStyleSheets.length; ++i) {
-    if (docStyleSheets[i].title == title)
-      return true;
-  }
-  return false;
+  return Array.some(frame.document.styleSheets,
+                    function (stylesheet) stylesheet.title == title);
 }
 
 function stylesheetSwitchFrame(frame, title) {
   var docStyleSheets = frame.document.styleSheets;
 
-  for (var i = 0; i < docStyleSheets.length; ++i) {
-    var docStyleSheet = docStyleSheets[i];
+  for (let i = 0; i < docStyleSheets.length; ++i) {
+    let docStyleSheet = docStyleSheets[i];
 
     if (title == "_nostyle")
       docStyleSheet.disabled = true;
@@ -5199,18 +5183,16 @@ function stylesheetSwitchFrame(frame, title) {
 }
 
 function stylesheetSwitchAll(frameset, title) {
-  if (!title || title == "_nostyle" || stylesheetInFrame(frameset, title)) {
+  if (!title || title == "_nostyle" || stylesheetInFrame(frameset, title))
     stylesheetSwitchFrame(frameset, title);
-  }
-  for (var i = 0; i < frameset.frames.length; i++) {
+
+  for (let i = 0; i < frameset.frames.length; i++)
     stylesheetSwitchAll(frameset.frames[i], title);
-  }
 }
 
 function setStyleDisabled(disabled) {
   getMarkupDocumentViewer().authorStyleDisabled = disabled;
 }
-
 /* End of the Page Style functions */
 
 var BrowserOffline = {