--- a/uriloader/exthandler/nsExternalHelperAppService.cpp
+++ b/uriloader/exthandler/nsExternalHelperAppService.cpp
@@ -1149,16 +1149,22 @@ NS_IMETHODIMP nsExternalAppHandler::GetT
 }
 
 NS_IMETHODIMP nsExternalAppHandler::GetTimeDownloadStarted(PRTime* aTime)
 {
   *aTime = mTimeDownloadStarted;
   return NS_OK;
 }
 
+NS_IMETHODIMP nsExternalAppHandler::GetContentLength(PRInt64 *aContentLength)
+{
+  *aContentLength = mContentLength;
+  return NS_OK;
+}
+
 NS_IMETHODIMP nsExternalAppHandler::CloseProgressWindow()
 {
   // release extra state...
   mWebProgressListener = nsnull;
   return NS_OK;
 }
 
 void nsExternalAppHandler::RetargetLoadNotifications(nsIRequest *request)

--- a/uriloader/exthandler/nsIExternalHelperAppService.idl
+++ b/uriloader/exthandler/nsIExternalHelperAppService.idl
@@ -161,9 +161,14 @@ interface nsIHelperAppLauncher : nsICanc
    * The executable-ness of the target file
    */
   readonly attribute boolean targetFileIsExecutable;
 
   /**
    * Time when the download started
    */
   readonly attribute PRTime timeDownloadStarted;
+
+  /**
+   * The download content length, or -1 if the length is not available.
+   */
+  readonly attribute PRInt64 contentLength;
 };