htmlArea RTE: Use parentNode rather than parentElement
While investigation issue #23778 and making a workaround I've noted that the "parentElement" property of a DOM element is used. This property is not supported in Firefox (Gecko) as it's proprietary [http://msdn.microsoft.com/en-us/library/ms534327(VS.85).aspx] and therefore it should not be used.
EXT:rtehtmlarea/htmlarea/plugins/TableOperations/table-operations.js line 1044 should be changed to
var tr = cell.parentNode;
This makes is possible to handle merging of table cells consistently across browsers (see issue #23778).
(issue imported from #M16975)