diff --git a/xpcom/io/nsIFile.idl b/xpcom/io/nsIFile.idl
index c18e28ac4799..3841bd7b3cd5 100644
--- a/xpcom/io/nsIFile.idl
+++ b/xpcom/io/nsIFile.idl
@@ -16,6 +16,7 @@
 [ptr] native FILE(FILE);
 
 interface nsISimpleEnumerator;
+interface nsIFileUpdateListener;
 
 /**
  * This is the only correct cross-platform way to specify a file.
@@ -30,7 +31,7 @@ interface nsISimpleEnumerator;
  * be safely passed to javascript via xpconnect.  Therefore, the "native
  * methods" are not scriptable. 
  */
-[scriptable, uuid(272a5020-64f5-485c-a8c4-44b2882ae0a2), builtinclass]
+[scriptable, uuid(9117c043-c01b-487a-a7ad-32cb350b0971), builtinclass]
 interface nsIFile : nsISupports
 {
     /**
@@ -447,6 +448,62 @@ interface nsIFile : nsISupports
      *       the relative descriptor obtained from getRelativeDescriptor
      */
     void setRelativeDescriptor(in nsIFile fromFile, in ACString relativeDesc);    
+
+    /**
+     *  watch
+     *
+     *  Watches this file for changes, or if this nsIFile is a
+     *  directory, watch for changes in its children recursively, not
+     *  dereferencing symlinks.  Multiple listeners can be installed
+     *  at once, and all will be called when any appropriate changes
+     *  are made.  If a child directory is created, that directory
+     *  will automatically be watched. If the file is a symlink to a
+     *  directory or another file, the target will be watched for
+     *  changes, not the link.
+     *
+     *  @param listener
+     *      The listener to call out to when the file updates.
+     *      Updated will be recieved on the main thread.
+     *
+     *  @return NS_ERROR_FILE_TARGET_DOES_NOT_EXIST if the file
+     *          doesn't exist, NS_NOT_AVAILABLE if there is an
+     *          out-of-memory or other resource failure, NS_OK
+     *          otherwise.
+     */
+    void watch(in nsIFileUpdateListener listener);
+
+    /**
+     *
+     *  unwatch
+     *
+     *  Removes the watch using the given listener from the file.
+     *  After this function terminates, no more requests will call the
+     *  given listener.
+     *
+     *  @param listener
+     *      the listener to stop calling out to
+     *
+     *  @return NS_ERROR_ILLEGAL_VALUE if the file is not being
+     *          watched with the given listener, NS_OK otherwise.
+     */
+    void unwatch(in nsIFileUpdateListener listener);
+};
+
+[scriptable, uuid(8968aaba-0f95-436c-8baf-7092ccaa814c), function]
+interface nsIFileUpdateListener : nsISupports
+{
+    /**
+     *  update
+     *
+     *  This function will be called whenever there is an update to be
+     *  processed.
+     *
+     *  @param type
+     *      The type of update that occured (one of "created" "deleted" "modified" or "unknown").
+     *  @param file
+     *      The file which has updated
+     */
+    void update(in string type, in nsIFile file);
 };
 
 %{C++
diff --git a/xpcom/io/nsLocalFileCommon.cpp b/xpcom/io/nsLocalFileCommon.cpp
index a36e0b534d6a..fb4fafbec0f3 100644
--- a/xpcom/io/nsLocalFileCommon.cpp
+++ b/xpcom/io/nsLocalFileCommon.cpp
@@ -13,12 +13,12 @@
 #include "nsCRT.h"
 #include "nsNativeCharsetUtils.h"
 #include "nsUTF8Utils.h"
+#include "nsThreadUtils.h"
 
 #ifdef XP_WIN
 #include <string.h>
 #endif
 
-
 void NS_StartupLocalFile()
 {
     nsLocalFile::GlobalInit();
@@ -288,3 +288,17 @@ nsLocalFile::SetRelativeDescriptor(nsIFile *fromFile, const nsACString& relative
 
     return InitWithFile(targetFile);
 }
+
+NS_IMETHODIMP
+nsLocalFile::Watch(nsIFileUpdateListener *listener)
+{
+    NS_ASSERTION(NS_IsMainThread(), "Watch must be called from main thread!");
+    return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+nsLocalFile::Unwatch(nsIFileUpdateListener *listener)
+{
+    NS_ASSERTION(NS_IsMainThread(), "Unwatch must be called from main thread!");
+    return NS_ERROR_NOT_IMPLEMENTED;
+}