Hello everybody. Here's my simple userscript, that highlights viewed submits in tables.
PavelKunyavskiy suggested to make it public.
Because it's not good to send additional AJAX queries to the server, functionality is quite little. Submit becomes marked after opening it's table cell. Unique-hash of submit is (user, problem, time), so submits, made in same minute, seems identical. I don't think it's a big problem :-)
Everybody who doesn't like default style can adjust it in function
It works in Firefox in Greasemonkey, in Chrome by default. Don't know about Opera, though.
I can improve something. Use it :-)
UPD1: Now by ctrl-click as good as by double-click
UPD2: Now works under Opera.