diff --git a/embedding/components/ui/progressDlg/nsProgressDialog.js b/embedding/components/ui/progressDlg/nsProgressDialog.js
index 2c78f68aaf35..877735ec7390 100644
--- a/embedding/components/ui/progressDlg/nsProgressDialog.js
+++ b/embedding/components/ui/progressDlg/nsProgressDialog.js
@@ -72,7 +72,7 @@ function nsProgressDialog() {
     this.mRequest     = null;
     this.mCompleted   = false;
     this.mMode        = "normal";
-    this.mPercent     = 0;
+    this.mPercent     = -1;
     this.mRate        = 0;
     this.mBundle      = null;
     this.mCancelDownloadOnClose = true;