diff --git a/mozilla/content/html/document/src/nsMediaDocument.cpp b/mozilla/content/html/document/src/nsMediaDocument.cpp
index c9b5449f487..4c90eb36aa9 100644
--- a/mozilla/content/html/document/src/nsMediaDocument.cpp
+++ b/mozilla/content/html/document/src/nsMediaDocument.cpp
@@ -322,10 +322,11 @@ nsMediaDocument::UpdateTitleAndCharset(const nsACString& aTypeStr,
       nsCOMPtr<nsITextToSubURI> textToSubURI = 
         do_GetService(NS_ITEXTTOSUBURI_CONTRACTID, &rv);
       if (NS_SUCCEEDED(rv))
-        rv = textToSubURI->UnEscapeURIForUI(docCharset, fileName, fileStr);
+        // UnEscapeURIForUI always succeeds
+        textToSubURI->UnEscapeURIForUI(docCharset, fileName, fileStr);
+      else 
+        CopyUTF8toUTF16(fileName, fileStr);
     }
-    if (fileStr.IsEmpty())
-      CopyUTF8toUTF16(fileName, fileStr);
   }
 
 
diff --git a/mozilla/docshell/base/nsDocShell.cpp b/mozilla/docshell/base/nsDocShell.cpp
index 73aa578e208..c06b967003c 100644
--- a/mozilla/docshell/base/nsDocShell.cpp
+++ b/mozilla/docshell/base/nsDocShell.cpp
@@ -2835,11 +2835,11 @@ nsDocShell::DisplayLoadError(nsresult aError, nsIURI *aURI,
         nsCOMPtr<nsITextToSubURI> textToSubURI(
                 do_GetService(NS_ITEXTTOSUBURI_CONTRACTID, &rv));
         if (NS_SUCCEEDED(rv))
-          rv = textToSubURI->UnEscapeURIForUI(charset, spec, formatStrs[0]);
-        if (NS_FAILED(rv)) {
-          CopyASCIItoUCS2(spec, formatStrs[0]);
-          rv = NS_OK;
-        }
+            // UnEscapeURIForUI always succeeds 
+            textToSubURI->UnEscapeURIForUI(charset, spec, formatStrs[0]);
+        else 
+            CopyUTF8toUTF16(spec, formatStrs[0]);
+        rv = NS_OK;
         formatStrCount = 1;
         error.AssignLiteral("fileNotFound");
     }
diff --git a/mozilla/intl/uconv/idl/nsITextToSubURI.idl b/mozilla/intl/uconv/idl/nsITextToSubURI.idl
index 509921c3507..938cc46163f 100644
--- a/mozilla/intl/uconv/idl/nsITextToSubURI.idl
+++ b/mozilla/intl/uconv/idl/nsITextToSubURI.idl
@@ -52,14 +52,18 @@ interface nsITextToSubURI : nsISupports
 
   /**
    * Unescapes the given URI fragment (for UI purpose only)
-   * note: escaping back the result unescaped string is not guaranteed to be
-   * identical to the original escaped string
+   * Note: 
+   * <ul>
+   *  <li> escaping back the result (unescaped string) is not guaranteed to 
+   *       give the original escaped string
+   *  <li> In case of a conversion error, the URI fragment (escaped) is 
+   *       assumed to be in UTF-8 and converted to AString (UTF-16)
+   *  <li> Always succeeeds (callers don't need to do error checking)
+   * </ul>
    *
    * @param aCharset the charset to convert from
    * @param aURIFragment the URI (or URI fragment) to unescape
    * @return Unescaped aURIFragment  converted to unicode
-   * @throws NS_ERROR_UCONV_NOCONV when there is no decoder for aCharset
-   *         or error code of nsIUnicodeDecoder in case of covnersion failure
    */
   AString unEscapeURIForUI(in ACString aCharset, in AUTF8String aURIFragment);
 
diff --git a/mozilla/intl/uconv/src/nsTextToSubURI.cpp b/mozilla/intl/uconv/src/nsTextToSubURI.cpp
index 1373a230149..af8879d57d6 100644
--- a/mozilla/intl/uconv/src/nsTextToSubURI.cpp
+++ b/mozilla/intl/uconv/src/nsTextToSubURI.cpp
@@ -230,7 +230,12 @@ NS_IMETHODIMP  nsTextToSubURI::UnEscapeURIForUI(const nsACString & aCharset,
   NS_UnescapeURL(PromiseFlatCString(aURIFragment), 
                  esc_SkipControl | esc_AlwaysCopy, unescapedSpec);
 
-  return convertURItoUnicode(PromiseFlatCString(aCharset), unescapedSpec, PR_TRUE, _retval);
+  // in case of failure, return escaped URI
+  if (NS_FAILED(convertURItoUnicode(
+                PromiseFlatCString(aCharset), unescapedSpec, PR_TRUE, _retval)))
+    // assume UTF-8 instead of ASCII  because hostname (IDN) may be in UTF-8
+    CopyUTF8toUTF16(aURIFragment, _retval); 
+  return NS_OK;
 }
 
 NS_IMETHODIMP  nsTextToSubURI::UnEscapeNonAsciiURI(const nsACString & aCharset,