--- a/toolkit/components/osfile/osfile_shared_front.jsm
+++ b/toolkit/components/osfile/osfile_shared_front.jsm
@@ -186,16 +186,30 @@ AbstractFile.normalizeToPointer = functi
   }
   if (offset != 0) {
     ptr = exports.OS.Shared.offsetBy(ptr, offset);
   }
   return {ptr: ptr, bytes: bytes};
 };
 
 /**
+ * Code shared by iterators.
+ */
+AbstractFile.AbstractIterator = function AbstractIterator() {
+};
+AbstractFile.AbstractIterator.prototype = {
+  /**
+   * Allow iterating with |for|
+   */
+  __iterator__: function __iterator__() {
+    return this;
+  }
+};
+
+/**
  * Utility function shared by implementations of |OS.File.open|:
  * extract read/write/trunc/create/existing flags from a |mode|
  * object.
  *
  * @param {*=} mode An object that may contain fields |read|,
  * |write|, |truncate|, |create|, |existing|. These fields
  * are interpreted only if true-ish.
  * @return {{read:bool, write:bool, trunc:bool, create:bool,

--- a/toolkit/components/osfile/osfile_unix_front.jsm
+++ b/toolkit/components/osfile/osfile_unix_front.jsm
@@ -578,63 +578,61 @@
       * @param {string} path The directory upon which to iterate.
       * @param {*=} options Ignored in this implementation.
       *
       * @throws {File.Error} If |path| does not represent a directory or
       * if the directory cannot be iterated.
       * @constructor
       */
      File.DirectoryIterator = function DirectoryIterator(path, options) {
+       exports.OS.Shared.AbstractFile.AbstractIterator.call(this);
        let dir = throw_on_null("DirectoryIterator", UnixFile.opendir(path));
        this._dir = dir;
        this._path = path;
      };
-     File.DirectoryIterator.prototype = {
-       __iterator__: function __iterator__() {
-         return this;
-       },
-       /**
-        * Return the next entry in the directory, if any such entry is
-        * available.
-        *
-        * Skip special directories "." and "..".
-        *
-        * @return {File.Entry} The next entry in the directory.
-        * @throws {StopIteration} Once all files in the directory have been
-        * encountered.
-        */
-       next: function next() {
-         if (!this._dir) {
-           throw StopIteration;
+     File.DirectoryIterator.prototype = Object.create(exports.OS.Shared.AbstractFile.AbstractIterator.prototype);
+
+     /**
+      * Return the next entry in the directory, if any such entry is
+      * available.
+      *
+      * Skip special directories "." and "..".
+      *
+      * @return {File.Entry} The next entry in the directory.
+      * @throws {StopIteration} Once all files in the directory have been
+      * encountered.
+      */
+     File.DirectoryIterator.prototype.next = function next() {
+       if (!this._dir) {
+         throw StopIteration;
+       }
+       for (let entry = UnixFile.readdir(this._dir);
+            entry != null && !entry.isNull();
+            entry = UnixFile.readdir(this._dir)) {
+         let contents = entry.contents;
+         if (contents.d_type == OS.Constants.libc.DT_DIR) {
+           let name = contents.d_name.readString();
+           if (name == "." || name == "..") {
+             continue;
+           }
          }
-         for (let entry = UnixFile.readdir(this._dir);
-              entry != null && !entry.isNull();
-              entry = UnixFile.readdir(this._dir)) {
-           let contents = entry.contents;
-           if (contents.d_type == OS.Constants.libc.DT_DIR) {
-             let name = contents.d_name.readString();
-             if (name == "." || name == "..") {
-               continue;
-             }
-           }
-           return new File.DirectoryIterator.Entry(contents, this._path);
-         }
-         this.close();
-         throw StopIteration;
-       },
+         return new File.DirectoryIterator.Entry(contents, this._path);
+       }
+       this.close();
+       throw StopIteration;
+     };
 
-       /**
-        * Close the iterator and recover all resources.
-        * You should call this once you have finished iterating on a directory.
-        */
-       close: function close() {
-         if (!this._dir) return;
-         UnixFile.closedir(this._dir);
-         this._dir = null;
-       }
+     /**
+      * Close the iterator and recover all resources.
+      * You should call this once you have finished iterating on a directory.
+      */
+     File.DirectoryIterator.prototype.close = function close() {
+       if (!this._dir) return;
+       UnixFile.closedir(this._dir);
+       this._dir = null;
      };
 
      /**
       * An entry in a directory.
       */
      File.DirectoryIterator.Entry = function Entry(unix_entry, parent) {
        // Copy the relevant part of |unix_entry| to ensure that
        // our data is not overwritten prematurely.

--- a/toolkit/components/osfile/osfile_win_front.jsm
+++ b/toolkit/components/osfile/osfile_win_front.jsm
@@ -475,36 +475,34 @@
       * @param {string} path The directory upon which to iterate.
       * @param {*=} options Ignored in this implementation.
       *
       * @throws {File.Error} If |path| does not represent a directory or
       * if the directory cannot be iterated.
       * @constructor
       */
      File.DirectoryIterator = function DirectoryIterator(path, options) {
+       exports.OS.Shared.AbstractFile.AbstractIterator.call(this);
        if (options && options.winPattern) {
          this._pattern = path + "\\" + options.winPattern;
        } else {
          this._pattern = path + "\\*";
        }
        this._handle = null;
        this._path = path;
        this._started = false;
      };
-     File.DirectoryIterator.prototype = {
-       __iterator__: function __iterator__() {
-         return this;
-       },
+     File.DirectoryIterator.prototype = Object.create(exports.OS.Shared.AbstractFile.AbstractIterator.prototype);
 
        /**
         * Fetch the next entry in the directory.
         *
         * @return null If we have reached the end of the directory.
         */
-       _next: function _next() {
+     File.DirectoryIterator.prototype._next = function _next() {
          // Iterator is not fully initialized yet. Finish
          // initialization.
          if (!this._started) {
             this._started = true;
             this._handle = WinFile.FindFirstFile(this._pattern, gFindDataPtr);
             if (this._handle == null) {
               let error = ctypes.winLastError;
               if (error == Const.ERROR_FILE_NOT_FOUND) {
@@ -539,37 +537,36 @@
         * available.
         *
         * Skip special directories "." and "..".
         *
         * @return {File.Entry} The next entry in the directory.
         * @throws {StopIteration} Once all files in the directory have been
         * encountered.
         */
-       next: function next() {
+     File.DirectoryIterator.prototype.next = function next() {
          // FIXME: If we start supporting "\\?\"-prefixed paths, do not forget
          // that "." and ".." are absolutely normal file names if _path starts
          // with such prefix
          for (let entry = this._next(); entry != null; entry = this._next()) {
            let name = entry.cFileName.readString();
            if (name == "." || name == "..") {
              continue;
            }
            return new File.DirectoryIterator.Entry(entry, this._path);
          }
          throw StopIteration;
-       },
-       close: function close() {
-         if (!this._handle) {
-           return;
-         }
-         throw_on_zero("FindClose",
-           WinFile.FindClose(this._handle));
-         this._handle = null;
+     };
+     File.DirectoryIterator.prototype.close = function close() {
+       if (!this._handle) {
+         return;
        }
+       throw_on_zero("FindClose",
+         WinFile.FindClose(this._handle));
+       this._handle = null;
      };
      File.DirectoryIterator.Entry = function Entry(win_entry, parent) {
        // Copy the relevant part of |win_entry| to ensure that
        // our data is not overwritten prematurely.
        if (!win_entry.dwFileAttributes) {
          throw new TypeError();
        }
        this._dwFileAttributes = win_entry.dwFileAttributes;