--- a/b2g/app/b2g.js
+++ b/b2g/app/b2g.js
@@ -843,10 +843,13 @@ pref("b2g.neterror.url", "app://system.g
 
 // Enable Web Speech synthesis API
 pref("media.webspeech.synth.enabled", true);
 
 // Downloads API
 pref("dom.mozDownloads.enabled", true);
 pref("dom.downloads.max_retention_days", 7);
 
+// Inactivity time in milliseconds after which we shut down the OS.File worker.
+pref("osfile.reset_worker_delay", 5000);
+
 // The URL of the Firefox Accounts auth server backend
 pref("identity.fxaccounts.auth.uri", "https://api-accounts.dev.lcip.org/v1");

--- a/toolkit/components/osfile/modules/osfile_async_front.jsm
+++ b/toolkit/components/osfile/modules/osfile_async_front.jsm
@@ -22,16 +22,17 @@
 this.EXPORTED_SYMBOLS = ["OS"];
 
 const Cu = Components.utils;
 const Ci = Components.interfaces;
 
 let SharedAll = {};
 Cu.import("resource://gre/modules/osfile/osfile_shared_allthreads.jsm", SharedAll);
 Cu.import("resource://gre/modules/Deprecated.jsm", this);
+Cu.import("resource://gre/modules/Timer.jsm", this);
 
 // Boilerplate, to simplify the transition to require()
 let LOG = SharedAll.LOG.bind(SharedAll, "Controller");
 let isTypedArray = SharedAll.isTypedArray;
 
 // The constructor for file errors.
 let SysAll = {};
 if (SharedAll.Constants.Win) {
@@ -112,16 +113,36 @@ let Scheduler = {
    */
   shutdown: false,
 
   /**
    * The latest promise returned.
    */
   latestPromise: Promise.resolve("OS.File scheduler hasn't been launched yet"),
 
+  /**
+   * A timer used to automatically shut down the worker after some time.
+   */
+  resetTimer: null,
+
+  restartTimer: function(arg) {
+    let delay;
+    try {
+      delay = Services.prefs.getIntPref("osfile.reset_worker_delay");
+    } catch(e) {
+      // Don't auto-shutdown if we don't have a delay preference set.
+      return;
+    }
+
+    if (this.resetTimer) {
+      clearTimeout(this.resetTimer);
+    }
+    this.resetTimer = setTimeout(File.resetWorker, delay);
+  },
+
   post: function post(...args) {
     if (this.shutdown) {
       LOG("OS.File is not available anymore. The following request has been rejected.", args);
       return Promise.reject(new Error("OS.File has been shut down."));
     }
     if (!worker) {
       // Either the worker has never been created or it has been reset
       worker = new PromiseWorker(
@@ -134,16 +155,22 @@ let Scheduler = {
     this.launched = true;
 
     // By convention, the last argument of any message may be an |options| object.
     let methodArgs = args[1];
     let options = methodArgs ? methodArgs[methodArgs.length - 1] : null;
     let promise = worker.post.apply(worker, args);
     return this.latestPromise = promise.then(
       function onSuccess(data) {
+        // Don't restart the timer when reseting the worker, since that will
+        // lead to an endless "resetWorker()" loop.
+        if (args[0] != "Meta_reset") {
+          Scheduler.restartTimer();
+        }
+
         // Check for duration and return result.
         if (!options) {
           return data.ok;
         }
         // Check for options.outExecutionDuration.
         if (typeof options !== "object" ||
           !("outExecutionDuration" in options)) {
           return data.ok;
@@ -162,16 +189,22 @@ let Scheduler = {
         if (typeof options.outExecutionDuration == "number") {
           options.outExecutionDuration += durationMs;
         } else {
           options.outExecutionDuration = durationMs;
         }
         return data.ok;
       },
       function onError(error) {
+        // Don't restart the timer when reseting the worker, since that will
+        // lead to an endless "resetWorker()" loop.
+        if (args[0] != "Meta_reset") {
+          Scheduler.restartTimer();
+        }
+
         // Decode any serialized error
         if (error instanceof PromiseWorker.WorkerError) {
           throw OS.File.Error.fromMsg(error.data);
         }
         // Extract something meaningful from ErrorEvent
         if (error instanceof ErrorEvent) {
           let message = error.message;
           if (message == "uncaught exception: [object StopIteration]") {