--- a/toolkit/components/osfile/osfile_shared_front.jsm
+++ b/toolkit/components/osfile/osfile_shared_front.jsm
@@ -196,16 +196,32 @@ AbstractFile.normalizeToPointer = functi
 AbstractFile.AbstractIterator = function AbstractIterator() {
 };
 AbstractFile.AbstractIterator.prototype = {
   /**
    * Allow iterating with |for|
    */
   __iterator__: function __iterator__() {
     return this;
+  },
+  /**
+   * Apply a function to all elements of the directory sequentially.
+   *
+   * @param {Function} cb This function will be applied to all entries
+   * of the directory. It receives as arguments
+   *  - the OS.File.Entry corresponding to the entry;
+   *  - the index of the entry in the enumeration;
+   *  - the iterator itself - calling |close| on the iterator stops
+   *   the loop.
+   */
+  forEach: function forEach(cb) {
+    let index = 0;
+    for (let entry in this) {
+      cb(entry, index++, this);
+    }
   }
 };
 
 /**
  * Utility function shared by implementations of |OS.File.open|:
  * extract read/write/trunc/create/existing flags from a |mode|
  * object.
  *