apply patch from Tomi Leppikangas <Tomi.Leppikangas@oulu.fi> to fix

nsTextHelper::SetText()

widget/src/gtk/nsTextHelper.cpp

@@ -101,7 +101,10 @@ NS_METHOD  nsTextHelper::SetText(const nsString& aText, PRUint32& aActualSize)
   if (GTK_IS_ENTRY(mWidget)) {
     gtk_entry_set_text(GTK_ENTRY(mWidget), buf);
   } else if (GTK_IS_TEXT(mWidget)) {
-    gtk_text_insert(GTK_TEXT(mWidget), nsnull, nsnull, nsnull, buf, aText.Length());
+    gtk_editable_delete_text(GTK_EDITABLE(mWidget), 0,
+                             gtk_text_get_length(GTK_TEXT (mWidget)));
+    gtk_text_insert(GTK_TEXT(mWidget), nsnull, nsnull, nsnull,
+                    buf, aText.Length());
   }
 
   aActualSize = aText.Length();