Holy tap-dancing cat!
My cat does certain things to attract my attention, particularly if I'm ignoring him... shoving recently listened-to CDs off a pile, tearing up papers, pulling books out of the bookcases, sitting on top of a printer and peeking at me from the gap between the big copier/printer and the computer screen... but he's never opened 300 browser tabs. However, I wouldn't put it past him. There is probably a secret cat society where cats from all over the world tell each other what actions lead to their owner's/subject's most notable reactions.
It's either that, or your cat was trying to filter out many many many many many an eBay listing. Or... as you've suggested... tapdancing.
