When adding rows to large tables, (in excessive of around 500 rows), there is a significant hang and often an unresponsive script error appears. My experiments show that the row is added after a substantial delay, (of upto 10 seconds), but our customer reports that the rows are not added at all.

No other browsers appear to be impacted by adding rows to tables that are this size, so this appears to be a Firefox specific issue, (which affects both v11 and v12).