I feel like I'm missing something so I probably am...
That code isn't triggering for anything because ff won't pick up 'rclass' (I assume it would if you were working in pure xml) and there are no appropriate ids set..?
(hug)
If you really want to pass the target-rowspan through a tag, maybe you could pass it through something valid where it won't do anything, like 'align' or maybe 'href' or something?
Either that or declare it as xml.