diff --git a/mozilla/xpcom/io/nsILocalFile.idl b/mozilla/xpcom/io/nsILocalFile.idl
index 75eef1442d7..c0dc6026d71 100644
--- a/mozilla/xpcom/io/nsILocalFile.idl
+++ b/mozilla/xpcom/io/nsILocalFile.idl
@@ -64,6 +64,18 @@ interface nsILocalFile : nsIFile
     [noscript] PRLibraryStar  load();
     
     readonly attribute PRInt64 diskSpaceAvailable;  // maybe we should put this somewhere else.
+
+    /**
+     * appendRelativePath
+     *
+     * Append a relative path to the current path of the nsILocalFile object.
+     *
+     * @param relativeFilePath
+     *        relativeFilePath is a native relative path. For security reasons,
+     *        this cannot contain ..	or cannot start with a directory separator
+     */
+    void appendRelativePath([const] in string relativeFilePath);
+    void appendRelativeUnicodePath([const] in wstring relativeFilePath);
 };
 
 %{C++
diff --git a/mozilla/xpcom/io/nsLocalFileCommon.cpp b/mozilla/xpcom/io/nsLocalFileCommon.cpp
index a63c0bcd77e..e65c779af38 100644
--- a/mozilla/xpcom/io/nsLocalFileCommon.cpp
+++ b/mozilla/xpcom/io/nsLocalFileCommon.cpp
@@ -240,6 +240,11 @@ nsLocalFile::AppendUnicode(const PRUnichar *node)
    SET_UCS( Append , node);
 }
 NS_IMETHODIMP  
+nsLocalFile::AppendRelativeUnicodePath(const PRUnichar *node)
+{
+   SET_UCS( AppendRelativePath , node);
+}
+NS_IMETHODIMP  
 nsLocalFile::GetUnicodeLeafName(PRUnichar **aLeafName)
 {
    GET_UCS(GetLeafName, aLeafName);
diff --git a/mozilla/xpcom/io/nsLocalFileMac.cpp b/mozilla/xpcom/io/nsLocalFileMac.cpp
index a0f92cc7276..aba6cd700ba 100644
--- a/mozilla/xpcom/io/nsLocalFileMac.cpp
+++ b/mozilla/xpcom/io/nsLocalFileMac.cpp
@@ -1119,9 +1119,18 @@ nsLocalFile::Create(PRUint32 type, PRUint32 attributes)
 
 	return NS_ERROR_FILE_UNKNOWN_TYPE;
 }
-	
+
 NS_IMETHODIMP  
 nsLocalFile::Append(const char *node)
+{
+  if (!node || (strstr(node, ":") != nsnull))
+    return NS_ERROR_FILE_UNRECOGNIZED_PATH;
+
+  return AppendRelativePath(node);
+}
+	
+NS_IMETHODIMP  
+nsLocalFile::AppendRelativePath(const char *node)
 {
 	if ( (node == nsnull) )
 		return NS_ERROR_FILE_UNRECOGNIZED_PATH;
diff --git a/mozilla/xpcom/io/nsLocalFileUnix.cpp b/mozilla/xpcom/io/nsLocalFileUnix.cpp
index 5df926d029c..c4512e8e3df 100644
--- a/mozilla/xpcom/io/nsLocalFileUnix.cpp
+++ b/mozilla/xpcom/io/nsLocalFileUnix.cpp
@@ -417,6 +417,28 @@ nsLocalFile::Append(const char *fragment)
 {
     NS_ENSURE_ARG(fragment);
     CHECK_mPath();
+
+    // only one component of path can be appended
+    if (strstr(fragment, "/") != nsnull)
+    {
+        return NS_ERROR_FILE_UNRECOGNIZED_PATH;
+    }
+
+    return AppendRelativePath(fragment);
+}
+
+NS_IMETHODIMP
+nsLocalFile::AppendRelativePath(const char *fragment)
+{
+    NS_ENSURE_ARG(fragment);
+    CHECK_mPath();
+
+    // Cannot start with a '/' and no .. allowed in the fragment
+    if ((*fragment == '/') || (strstr(fragment, "..") != nsnull))
+    {
+        return NS_ERROR_FILE_UNRECOGNIZED_PATH;
+    }
+
     char * newPath = (char *)nsAllocator::Alloc(strlen(mPath) +
                                                 strlen(fragment) + 2);
     if (!newPath)
diff --git a/mozilla/xpcom/io/nsLocalFileWin.cpp b/mozilla/xpcom/io/nsLocalFileWin.cpp
index a7a9e526119..38460e6a644 100644
--- a/mozilla/xpcom/io/nsLocalFileWin.cpp
+++ b/mozilla/xpcom/io/nsLocalFileWin.cpp
@@ -694,11 +694,20 @@ nsLocalFile::Create(PRUint32 type, PRUint32 attributes)
 NS_IMETHODIMP  
 nsLocalFile::Append(const char *node)
 {
-    if ( (node == nsnull)                                       ||
-         (*node == '/')                                         ||
-         (strstr(node, "..")                         != nsnull) ||
-         (_mbschr((const unsigned char*) node, '\\') != nsnull) ||
-         (strchr(node, '/')                          != nsnull) )
+    // Append only one component. Check for subdirs.
+    if (!node || (_mbschr((const unsigned char*) node, '\\') != nsnull))
+    {
+        return NS_ERROR_FILE_UNRECOGNIZED_PATH;
+    }
+    return AppendRelativePath(node);
+}
+
+NS_IMETHODIMP  
+nsLocalFile::AppendRelativePath(const char *node)
+{
+    // Cannot start with a / or have .. or have / anywhere
+    if (!node || (*node == '/') || (strstr(node, "..") != nsnull) ||
+        (strchr(node, '/') != nsnull))
     {
         return NS_ERROR_FILE_UNRECOGNIZED_PATH;
     }