diff --git a/toolkit/components/osfile/osfile_unix_back.jsm b/toolkit/components/osfile/osfile_unix_back.jsm
index 40d462d8c24..f2e34241dc5 100644
--- a/toolkit/components/osfile/osfile_unix_back.jsm
+++ b/toolkit/components/osfile/osfile_unix_back.jsm
@@ -2,23 +2,6 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this file,
  * You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-/**
- * This file can be used in the following contexts:
- *
- *  1. included from a non-osfile worker thread using importScript
- *   (it serves to define a synchronous API for that worker thread)
- *   (bug 707679)
- *
- *  2. included from the main thread using Components.utils.import
- *   (it serves to define the asynchronous API, whose implementation
- *    resides in the worker thread)
- *   (bug 729057)
- *
- * 3. included from the osfile worker thread using importScript
- *   (it serves to define the implementation of the asynchronous API)
- *   (bug 729057)
- */
-
 {
   if (typeof Components != "undefined") {
     // We do not wish osfile_unix_back.jsm to be used directly as a main thread
@@ -28,7 +11,8 @@
 
     throw new Error("osfile_unix_back.jsm cannot be used from the main thread yet");
   }
-  importScripts("resource://gre/modules/osfile/osfile_shared.jsm");
+  importScripts("resource://gre/modules/osfile/osfile_shared_allthreads.jsm");
+  importScripts("resource://gre/modules/osfile/osfile_unix_allthreads.jsm");
   (function(exports) {
      "use strict";
      if (!exports.OS) {
@@ -42,36 +26,21 @@
      }
      exports.OS.Unix.File = {};
 
-     let LOG = OS.Shared.LOG.bind(OS.Shared, "Unix");
-
-     // Open libc
-     let libc;
-     let libc_candidates =  [ "libsystem.B.dylib",
-                              "libc.so.6",
-                              "libc.so" ];
-     for (let i = 0; i < libc_candidates.length; ++i) {
-       try {
-         libc = ctypes.open(libc_candidates[i]);
-         break;
-       } catch (x) {
-         LOG("Could not open libc "+libc_candidates[i]);
-       }
-     }
-     if (!libc) {
-       throw new Error("Could not open any libc.");
-     }
+     let LOG = exports.OS.Shared.LOG.bind(OS.Shared, "Unix", "back");
+     let libc = exports.OS.Shared.Unix.libc;
 
      /**
       * Initialize the Unix module.
       *
       * @param {function=} declareFFI
       */
+     // FIXME: Both |init| and |aDeclareFFI| are deprecated, we should remove them
      let init = function init(aDeclareFFI) {
        let declareFFI;
        if (aDeclareFFI) {
          declareFFI = aDeclareFFI.bind(null, libc);
        } else {
-         declareFFI = OS.Shared.declareFFI.bind(null, libc);
+         declareFFI = exports.OS.Shared.Unix.declareFFI;
        }
 
        // Shorthands
@@ -468,11 +437,6 @@
                     /*len*/    Types.size_t,
                     /*flags*/  Types.unsigned_int); // Linux/Android-specific
 
-       UnixFile.strerror =
-         declareFFI("strerror", ctypes.default_abi,
-                    /*return*/ Types.null_or_string,
-                    /*errnum*/ Types.int);
-
        UnixFile.symlink =
          declareFFI("symlink", ctypes.default_abi,
                     /*return*/ Types.negativeone_or_nothing,
@@ -594,12 +558,6 @@
          array[1] = ctypes.CDataFinalizer(_pipebuf[1], _close);
          return result;
        };
-
-       // Export useful stuff for extensibility
-
-       exports.OS.Unix.libc = libc;
-       exports.OS.Unix.declareFFI = declareFFI;
-
      };
      exports.OS.Unix.File._init = init;
    })(this);
diff --git a/toolkit/components/osfile/osfile_unix_front.jsm b/toolkit/components/osfile/osfile_unix_front.jsm
index a1232f0a130..33feb6da227 100644
--- a/toolkit/components/osfile/osfile_unix_front.jsm
+++ b/toolkit/components/osfile/osfile_unix_front.jsm
@@ -16,7 +16,6 @@
 
     throw new Error("osfile_unix_front.jsm cannot be used from the main thread yet");
   }
-  importScripts("resource://gre/modules/osfile/osfile_shared.jsm");
   importScripts("resource://gre/modules/osfile/osfile_unix_back.jsm");
   importScripts("resource://gre/modules/osfile/ospath_unix_back.jsm");
   (function(exports) {
@@ -173,59 +172,6 @@
        }
      };
 
-     /**
-      * A File-related error.
-      *
-      * To obtain a human-readable error message, use method |toString|.
-      * To determine the cause of the error, use the various |becauseX|
-      * getters. To determine the operation that failed, use field
-      * |operation|.
-      *
-      * Additionally, this implementation offers a field
-      * |unixErrno|, which holds the OS-specific error
-      * constant. If you need this level of detail, you may match the value
-      * of this field against the error constants of |OS.Constants.libc|.
-      *
-      * @param {string=} operation The operation that failed. If unspecified,
-      * the name of the calling function is taken to be the operation that
-      * failed.
-      * @param {number=} lastError The OS-specific constant detailing the
-      * reason of the error. If unspecified, this is fetched from the system
-      * status.
-      *
-      * @constructor
-      * @extends {OS.Shared.Error}
-      */
-     File.Error = function(operation, errno) {
-       operation = operation || "unknown operation";
-       OS.Shared.Error.call(this, operation);
-       this.unixErrno = errno || ctypes.errno;
-     };
-     File.Error.prototype = new OS.Shared.Error();
-     File.Error.prototype.toString = function toString() {
-       return "Unix error " + this.unixErrno +
-         " during operation " + this.operation +
-         " (" + UnixFile.strerror(this.unixErrno).readString() + ")";
-     };
-
-     /**
-      * |true| if the error was raised because a file or directory
-      * already exists, |false| otherwise.
-      */
-     Object.defineProperty(File.Error.prototype, "becauseExists", {
-       get: function becauseExists() {
-         return this.unixErrno == OS.Constants.libc.EEXISTS;
-       }
-     });
-     /**
-      * |true| if the error was raised because a file or directory
-      * does not exist, |false| otherwise.
-      */
-     Object.defineProperty(File.Error.prototype, "becauseNoSuchFile", {
-       get: function becauseNoSuchFile() {
-         return this.unixErrno == OS.Constants.libc.ENOENT;
-       }
-     });
 
      // Constant used to normalize options.
      const noOptions = {};
@@ -886,6 +832,8 @@
      File.POS_END = exports.OS.Constants.libc.SEEK_END;
 
      File.Unix = exports.OS.Unix.File;
+     File.Error = exports.OS.Shared.Unix.Error;
      exports.OS.File = File;
+
    })(this);
 }
diff --git a/toolkit/components/osfile/ospath_unix_back.jsm b/toolkit/components/osfile/ospath_unix_back.jsm
index 522e39bc8a6..318171233a2 100644
--- a/toolkit/components/osfile/ospath_unix_back.jsm
+++ b/toolkit/components/osfile/ospath_unix_back.jsm
@@ -14,6 +14,10 @@
  *   parse (see later);
  * - all path concatenations go through function |join|.
  */
+if (typeof Components != "undefined") {
+  var EXPORTED_SYMBOLS = ["OS"];
+  Components.utils.import("resource://gre/modules/osfile/osfile_unix_allthreads.jsm");
+}
 (function(exports) {
    "use strict";
    if (!exports.OS) {