--- a/toolkit/components/osfile/osfile_shared_allthreads.jsm
+++ b/toolkit/components/osfile/osfile_shared_allthreads.jsm
@@ -27,29 +27,30 @@
      // that everybody uses the same definition of |OS|.
      if (typeof Components != "undefined") {
        Components.utils.import("resource://gre/modules/ctypes.jsm");
        Components.classes["@mozilla.org/net/osfileconstantsservice;1"].
          getService(Components.interfaces.nsIOSFileConstantsService).init();
      }
 
      // Define a lazy getter for a property
-     let defineLazyGetter = function(object, name, getter) {
+     let defineLazyGetter = function defineLazyGetter(object, name, getter) {
        Object.defineProperty(object, name, {
          configurable: true,
          get: function lazy() {
            delete this[name];
            let value = getter.call(this);
            Object.defineProperty(object, name, {
              value: value
            });
            return value;
          }
        });
      };
+     exports.OS.Shared.defineLazyGetter = defineLazyGetter;
 
      /**
       * A variable controlling whether we should printout logs.
       */
      exports.OS.Shared.DEBUG = false;
      let LOG;
      if (typeof console != "undefined" && console.log) {
        LOG = console.log.bind(console, "OS");

--- a/toolkit/components/osfile/osfile_win_back.jsm
+++ b/toolkit/components/osfile/osfile_win_back.jsm
@@ -67,54 +67,49 @@
        if (!exports.OS.Types) {
          exports.OS.Types = {};
        }
        let Type = exports.OS.Shared.Type;
        let Types = Type;
 
        // Initialize types
 
-       Types.HANDLE =
-         Types.voidptr_t.withName("HANDLE");
-
        /**
         * A C integer holding INVALID_HANDLE_VALUE in case of error or
         * a file descriptor in case of success.
         */
-       Types.maybe_HANDLE =
-         Types.HANDLE.withName("maybe_HANDLE");
-       Types.maybe_HANDLE.importFromC =
-         function maybe_HANDLE_importFromC(maybe) {
-           if (Types.int.cast(maybe).value == INVALID_HANDLE) {
-             // Ensure that API clients can effectively compare against
-             // Const.INVALID_HANDLE_VALUE. Without this cast,
-             // == would always return |false|.
-             return INVALID_HANDLE;
-           }
-         return ctypes.CDataFinalizer(maybe, _CloseHandle);
+       Types.HANDLE =
+         Types.voidptr_t.withName("HANDLE");
+       Types.HANDLE.importFromC = function importFromC(maybe) {
+         if (Types.int.cast(maybe).value == INVALID_HANDLE) {
+           // Ensure that API clients can effectively compare against
+           // Const.INVALID_HANDLE_VALUE. Without this cast,
+           // == would always return |false|.
+           return INVALID_HANDLE;
+         }
+         return ctypes.CDataFinalizer(maybe, this.finalizeHANDLE);
        };
+       Types.HANDLE.finalizeHANDLE = function placeholder() {
+         throw new Error("finalizeHANDLE should be implemented");
+       };
+       let INVALID_HANDLE = exports.OS.Constants.Win.INVALID_HANDLE_VALUE;
 
-       /**
-        * A C integer holding INVALID_HANDLE_VALUE in case of error or
-        * a file descriptor in case of success.
-        */
-       Types.maybe_find_HANDLE =
-         Types.HANDLE.withName("maybe_find_HANDLE");
-       Types.maybe_find_HANDLE.importFromC =
-         function maybe_find_HANDLE_importFromC(maybe) {
-           if (Types.int.cast(maybe).value == INVALID_HANDLE) {
-             // Ensure that API clients can effectively compare against
-             // Const.INVALID_HANDLE_VALUE. Without this cast,
-             // == would always return |false|.
-             return INVALID_HANDLE;
-           }
-         return ctypes.CDataFinalizer(maybe, _FindClose);
-       };
+       Types.file_HANDLE = Types.HANDLE.withName("file HANDLE");
+       exports.OS.Shared.defineLazyGetter(Types.file_HANDLE,
+         "finalizeHANDLE",
+         function() {
+           return _CloseHandle;
+         });
 
-       let INVALID_HANDLE = exports.OS.Constants.Win.INVALID_HANDLE_VALUE;
+       Types.find_HANDLE = Types.HANDLE.withName("find HANDLE");
+       exports.OS.Shared.defineLazyGetter(Types.find_HANDLE,
+         "finalizeHANDLE",
+         function() {
+           return _FindClose;
+         });
 
        Types.DWORD = Types.int32_t.withName("DWORD");
 
        /**
         * A C integer holding -1 in case of error or a positive integer
         * in case of success.
         */
        Types.negative_or_DWORD =
@@ -217,17 +212,17 @@
        WinFile.CreateDirectory =
          declareFFI("CreateDirectoryW", ctypes.winapi_abi,
                     /*return*/ Types.zero_or_nothing,
                     /*name*/   Types.jschar.in_ptr,
                     /*security*/Types.SECURITY_ATTRIBUTES.in_ptr);
 
        WinFile.CreateFile =
          declareFFI("CreateFileW", ctypes.winapi_abi,
-                    /*return*/  Types.maybe_HANDLE,
+                    /*return*/  Types.file_HANDLE,
                     /*name*/    Types.path,
                     /*access*/  Types.DWORD,
                     /*share*/   Types.DWORD,
                     /*security*/Types.SECURITY_ATTRIBUTES.in_ptr,
                     /*creation*/Types.DWORD,
                     /*flags*/   Types.DWORD,
                     /*template*/Types.HANDLE);
 
@@ -239,24 +234,24 @@
        WinFile.FileTimeToSystemTime =
          declareFFI("FileTimeToSystemTime", ctypes.winapi_abi,
                     /*return*/ Types.zero_or_nothing,
                     /*filetime*/Types.FILETIME.in_ptr,
                     /*systime*/ Types.SystemTime.out_ptr);
 
        WinFile.FindFirstFile =
          declareFFI("FindFirstFileW", ctypes.winapi_abi,
-                    /*return*/ Types.maybe_find_HANDLE,
+                    /*return*/ Types.find_HANDLE,
                     /*pattern*/Types.path,
                     /*data*/   Types.FindData.out_ptr);
 
        WinFile.FindNextFile =
          declareFFI("FindNextFileW", ctypes.winapi_abi,
                     /*return*/ Types.zero_or_nothing,
-                    /*prev*/   Types.HANDLE,
+                    /*prev*/   Types.find_HANDLE,
                     /*data*/   Types.FindData.out_ptr);
 
        WinFile.FormatMessage =
          declareFFI("FormatMessageW", ctypes.winapi_abi,
                     /*return*/ Types.DWORD,
                     /*flags*/  Types.DWORD,
                     /*source*/ Types.void_t.in_ptr,
                     /*msgid*/  Types.DWORD,